Method and apparatus for a searchable data service

0001This application claims priority to U.S. Provisional Patent Application Ser. No. 60/754,777, filed Dec. 29, 2005, and which is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

00021. Field of the Invention

0003This invention relates to data storage and retrieval, and, more particularly, to searchable indexes for data stores.

00042. Description of the Related Art

0005The Internet, sometimes called simply “the Net,” is a worldwide system of computer networks in which a client at any one computer may, with permission, obtain information from any other computer. The most widely used part of the Internet is the World Wide Web, often abbreviated “WWW”, which is commonly referred to as “the Web”. The Web may be defined as all the resources (e.g., Web pages and Web sites) and clients on the Internet that use the Hypertext Transfer Protocol (HTTP) or variations thereof to access the resources. A Web site is a related collection of Web files that includes a beginning file called a home page. From the home page, the client may navigate to other Web pages on the Web site. A Web server program is a program that, using the client/server model and HTTP, serves the files that form the Web pages of a Web site to the Web clients, whose computers contain HTTP client programs (e.g., Web browsers) that forward requests and display responses. A Web server program may host one or more Web sites.

0000Data Storage

0006Data storage, storing data objects of various types for access by various applications, is a primary area of interest and development in computer systems and applications, networking, the Internet, and related technical areas. Conventionally, developers have either created their own data storage solutions for storing data objects, have leveraged off-the-shelf database products, such as an Oracle/MySQL database, to develop data storage solutions, or have relied on third-party providers for data storage solutions. However the data storage solution is provided, data objects may be stored to, and retrieved from, the data store. Typically, a data storage solution provides one or more types of locators that may be used to retrieve data objects from the data store. A common “locator” is a file path-type locator, in which a client provides a file path, including a particular file name, to retrieve a particular data object (e.g., a file) from some location with a data store specified in the file path. File paths are, however, not very flexible, as the desired data object is specifiable only by the path/file name. File path mechanism, and other conventional “locator” mechanisms for retrieving data objects from data stores, typically do not provide the flexibility to retrieve data objects from a data store according to other attributes of the desired data objects. For example, a client may wish to retrieve data objects from the data store according to category, company, type, or any of countless other attributes that may be associated with a data object. Conventional file paths do not provide for such flexible retrieval methods.

0007There are “one-off” data storage solutions that may provide more flexible mechanisms for querying/retrieving data objects from a data store according to other attributes than just a file path/file name. Conventionally, different developers have tended to solve this same data storage problem for different applications over and over again in ways that do not scale to other problems, are not flexible to address other data storage needs, and/or have based their solutions on “off-the-shelf” technologies such as Oracle/MySQL that prove to be expensive in the short- and/or long-term. As the data store grows, these conventional data storage solutions generally require a data store administrator to perform or manage monitoring, partitioning, query optimizations, storage procedures, additions of new hardware, crisis/emergency procedures (e.g., when a storage system goes down), etc. In addition, for these conventional data storage solutions, if a client wants to add new attributes that may be used to query for and retrieve data objects, table schemas have to be changed to support the new attributes.

SUMMARY

0008Various embodiments of a method and apparatus for a general-purpose searchable data service are described. In one embodiment, the searchable data service may be implemented as a Web service that allows developers to store attributes, expressed as {name, value} pairs, that are associated with data objects (entities) stored in a data store. Attributes associated with entities may be automatically indexed for use in searches. Embodiments of the searchable data service may be implemented according to an architecture that is accessible to developers to develop search frontends to data stores for client applications, and to create and update searchable indexes to the data stores that are reliable, fast and scalable. The implementation of the searchable data service may be transparent to the client/developer. The client and/or developer only needs to be aware of a minimal, externally exposed interface to the searchable data service.

0009Embodiments of the searchable data service may provide a searchable index to a backend data store, and an interface to build and query the searchable index, that enables client applications to search for and retrieve locators for stored entities in the backend data store according to a list of attributes associated with each locator. The entities may be identified in a searchable index in the searchable data service by the locators for the entities. Each locator may have an associated set of attributes of the entity, expressed as {name, value} pairs. Note that the locator may itself be considered one of the attributes of the entity.

0010One embodiment of the searchable data service may be implemented as a Web service with a Web service interface that exposes one or more calls to the functionalities of the searchable data service to client applications. This Web service interface may enable developers to build search frontends for a variety of client applications that may access the functionalities of the searchable data service via the Web service interface to search for and retrieve locators for data entities stored in backend data stores. Applications that leverage the searchable data service as a search frontend for a data store may be automatically scaled to any size with little or no system administration overhead required for the scaling, and search speed may be automatically optimized using, for example, indexes, query planning, and parallelism.

0011The searchable data service provides a searchable index and is not itself a data store per se. Embodiments of the searchable data service may separate searching and indexing of data from the actual storage of the data. A backend data store may be implemented as any type of data storage system in which a locator may be used to locate and retrieve an entity, and may reside anywhere on a network, Local Area Network (LAN), Wide Area Network (WAN), or on the Internet, or may even be implemented on data storage locally attached to a computer system or systems. Embodiments of the searchable data service may be used to provide searchable indexes to any type of data. Embodiments may be used, for example, to provide searchable indexes to data stored in databases, and to repositories of files of various particular or mixed types including, but not limited to, textual, digital image, and digital audio files. Note, however, that embodiments of the searchable index may be used in applications where there may be no backend data store. In these applications, the attributes stored as {name, value} pairs in the searchable index are the data.

0012Embodiments of the searchable data service may include mechanisms that enable the searchable data service to scale easily, and to provide redundancy, reliability, and high availability of the searchable indexes without requiring any knowledge or additional effort by a developer of a client application. These mechanisms may include, but are not limited to, a mechanism for building the. searchable indexes, a mechanism for partitioning the searchable indexes, a mechanism for replicating the searchable indexes, a mechanism for handling the failure of nodes within the searchable data service, and a mechanism for the automated monitoring and control of nodes within the searchable data service.

0013Embodiments of the searchable data service may be implemented as a distributed system on a plurality of hosts, or nodes. In one embodiment, the nodes may include coordinator nodes that route requests from client systems to appropriate nodes within the searchable data service, query nodes that handle the processing of query requests, and storage nodes that store and manage the searchable index. In one embodiment, communications among nodes and components in a searchable data service implementation may be facilitated at least in part through a gossip protocol and an anti-entropy protocol.

BRIEF DESCRIPTION OF THE DRAWINGS

0015<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram that illustrates an exemplary system configuration that provides a Web service interface, and shows the interaction between a Web service client and a Web service provider.

0016<figref idref="DRAWINGS">FIG. 2</figref> illustrates the relationship and dataflow between a client and the searchable data service, according to one embodiment.

0017<figref idref="DRAWINGS">FIG. 3</figref> illustrates an exemplary high-level functional architecture for a searchable data service, according to one embodiment.

0018<figref idref="DRAWINGS">FIG. 4</figref> illustrates an exemplary network architecture for a searchable data service according to one embodiment.

0019<figref idref="DRAWINGS">FIGS. 5A and 5B</figref> illustrate a method for implementing a searchable data service that processes service requests to store searchable data service objects in a searchable index and to locate entity identifiers (eIDs) for entities in a data store in the searchable index according to one embodiment.

0020<figref idref="DRAWINGS">FIG. 6</figref> illustrates an exemplary lower-level, modular architecture for a searchable data service, according to one embodiment.

0021<figref idref="DRAWINGS">FIG. 7</figref> illustrates a method for partitioning a searchable index in a searchable data service system according to one embodiment.

0022<figref idref="DRAWINGS">FIG. 8</figref> illustrates a method for replicating a partition of a searchable index in a searchable data service system according to one embodiment.

0023<figref idref="DRAWINGS">FIGS. 9A and 9B</figref> illustrate searchable indexes for subscribers, the segregation of data (eIDs) for each subscriber into buckets, and partitioning of the buckets, according to one embodiment of the searchable data service.

0024<figref idref="DRAWINGS">FIG. 9C</figref> illustrates data replication via replicating partitions according to one embodiment.

0025<figref idref="DRAWINGS">FIG. 10</figref> illustrates the splitting of partitions in replication groups according to one embodiment.

0026<figref idref="DRAWINGS">FIG. 11</figref> illustrates an exemplary storage node and its components according to one embodiment.

0027<figref idref="DRAWINGS">FIG. 12</figref> illustrates various components of the searchable data service that may constitute or interact with the query subsystem to perform the servicing of queries from clients of the searchable data service, and further illustrates the data flow among the components, according to one embodiment.

0028<figref idref="DRAWINGS">FIG. 13</figref> illustrates an identifier circle, according to one embodiment.

0029<figref idref="DRAWINGS">FIG. 14</figref> illustrates an exemplary architecture for a single storage node according to one embodiment.

0030<figref idref="DRAWINGS">FIG. 15</figref> is a flowchart of a stress management method for a searchable data service system, according to one embodiment.

0031<figref idref="DRAWINGS">FIG. 16</figref> illustrates the life cycle of a replication group in a searchable data service according to one embodiment.

0032<figref idref="DRAWINGS">FIG. 17</figref> illustrates a method for monitoring group membership and health in a searchable data service system according to one embodiment.

0033<figref idref="DRAWINGS">FIG. 18</figref> illustrates a high-level architecture for an administrative console in a searchable data service system according to one embodiment.

0034<figref idref="DRAWINGS">FIG. 19</figref> illustrates an implementation of a searchable data service in a networked environment according to one embodiment.

0035<figref idref="DRAWINGS">FIG. 20</figref> is a block diagram illustrating an exemplary embodiment of a computer system on which embodiments may be implemented.

0036While the invention is described herein by way of example for several embodiments and illustrative drawings, those skilled in the art will recognize that the invention is not limited to the embodiments or drawings described. It should be understood, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include”, “including”, and “includes” mean including, but not limited to.

DETAILED DESCRIPTION OF EMBODIMENTS

0037Various embodiments of a method and apparatus for a general-purpose searchable data service are described. In one embodiment, the searchable data service may be implemented as a Web service that allows developers to store attributes, expressed as {name, value} pairs, that are associated with data objects (entities) in a data store. Attributes associated with entities may be automatically indexed for use in searches. Search expressions may perform logical and arithmetic operations on attributes to find and retrieve data objects, or entities, identified by locators (also referred to as entity identifiers, or eIDs) for the entities. Embodiments of the searchable data service may be implemented according to an architecture as described herein that is accessible to developers via a Web service interface to provide search frontends for client applications to data stores that are easy to implement, and to create and update searchable indexes to the data stores that are reliable, fast and scalable.

0038Embodiments of the searchable data service may provide a searchable index to a backend data store and an interface to build and query the searchable index that enable client applications to search for and retrieve locators for stored data (units of data, or data objects, in a data store may be referred to herein as entities) in the backend data store according to a list of attributes associated with each locator. The backend data store may be implemented as any type of data storage system in which a locator may be used to locate and retrieve an entity, and may store any type of data object (entity). The entities may be described in the searchable data service by locators for the entities in the data store, which may be referred to as entity Identifiers, or eIDs. Each locator, or eID, may have an associated set of attributes of the entity, expressed as {name, value} pairs. Note that the locator, or eID, may itself be considered one of the attributes of the entity in the data store. A query interface and protocol may be provided which may be used to query for and receive lists of eIDs from the searchable data service according to one or more of the attributes associated with the eIDs.

0039The conventional Web model allows clients to access Web resources (e.g., applications, services, and data) via an HTTP client program, such as a Web browser. A technology referred to as Web services may be used to provide programmatic access to Web resources. Web services may be used to provide Web software developers programmatic access to Web resources including technology platforms (e.g., applications and services) and data (e.g., product catalogs and other databases) hosted on Web-connected computers such as Web server systems via a Web service interface. Generally speaking, a Web service interface may be configured to provide a standard, cross-platform API (Application Programming Interface) for communication between a client requesting some service to be performed and the service provider. In some embodiments, a Web service interface may be configured to support the exchange of documents or messages including information describing the service request and response to that request. Such documents, or messages, may be exchanged using standardized Web protocols, such as the Hypertext Transfer Protocol (HTTP), for example, and may be formatted in a platform-independent data format, such as eXtensible Markup Language (XML), for example.

0040<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram that illustrates an exemplary system configuration that provides a Web service interface, and shows the interaction between a Web service client and a Web service provider. In this example, a Web service interface <b>106</b> may be implemented on a server <b>130</b> coupled to Internet <b>100</b>. This server <b>130</b> may be referred to as a Web service provider. Server <b>130</b>, or alternatively one or more other servers coupled to server <b>130</b>, may include one or more applications or services <b>108</b>. Server <b>130</b> may be coupled to data storage <b>140</b> for storing information in database <b>142</b>. Database <b>142</b> may include any type of data.

0041Server <b>120</b> may be coupled to Internet <b>100</b>. Server <b>120</b> may host a Web service client <b>124</b>. Web service client <b>124</b> may be configured to programmatically access application or service <b>108</b> of server <b>130</b> and/or database <b>142</b> via Web service interface <b>106</b>. Note that Web service interface does not provide a Web browser interface, but instead provides a programmatic interface via an API through which at least some functionality of application or service <b>108</b> and/or at least some data in database <b>142</b> may be programmatically accessed by Web service client <b>124</b>. Also note that server <b>120</b> may provide a Web site accessible to client(s) <b>122</b> via Web browsers, and Web service client <b>124</b> may be configured to access at least some functionality of application or service <b>108</b> and/or at least some data in database <b>142</b> of server <b>130</b> via Web service interface <b>106</b> to provide access to at least some functionality of application or service <b>108</b> and/or at least some data in database <b>142</b> via the Web site provided by server <b>120</b>. Further, note that Web service client <b>124</b> may itself be another Web service.

0042To access an application, service or data provided by the Web service provider <b>130</b>, Web service client <b>124</b> may send a request message to Web service interface <b>106</b> via Internet <b>100</b>. This request message goes through the network and Internet infrastructures; through the Web service client <b>124</b>'s local network routers, switches, firewalls, etc., through the Internet backbone, to the Web service provider's local network, to Server <b>130</b>, and then to Web service interface <b>106</b>. Web service provider <b>130</b> may then process the request, for example by performing an indicated function(s) of application or service <b>108</b> or accessing indicated data in database <b>142</b>. Web service interface <b>106</b> may then return results of the processing to the Web service client <b>124</b> in a response message via Internet <b>100</b>, back through the local networks and Internet backbone.

0043One embodiment of the searchable data service may be implemented as a Web service with a Web service interface that exposes one or more Web service calls to the functionalities of the searchable data service to client applications. This Web service interface may enable developers to easily build search frontends for a variety of client applications that access the functionalities of the searchable data service via the Web service interface to search for and retrieve various types of data stored in the backend data stores. Applications that leverage the searchable data service to implement a search frontend for a data store may be automatically scaled to any size with little or no system administration overhead required for the scaling, and search speed may be automatically optimized using, for example, indexes, query planning, and parallelism.

0044Embodiments of the searchable data service may provide an inexpensive, easy to implement, and easy to maintain searchable index and interface to the searchable index that may be leveraged to provide a search frontend to data stores that may satisfy the search requirements for a wide variety of applications. The searchable data service provides a searchable index and is not itself a data store per se. Embodiments of the searchable data service may separate searching and indexing of data from the actual storage of the data. A backend data store may be implemented as any type of data storage system in which a locator may be used to locate and retrieve an entity, and may reside anywhere on a network, Local Area Network (LAN), Wide Area Network (WAN), or on the Internet, or may even be implemented on a local data storage locally attached to a computer system or systems. Note, however, that embodiments of the searchable index may be used in applications where there may be no backend data store. In these applications, the attributes stored as {name, value} pairs in the searchable index are the data.

0045Embodiments of the searchable data service may enable developers to put the data store anywhere they want; the developers then provide the locators (eIDs) to the searchable data service, along with a set of attributes, expressed as {name, value} pairs, for the eIDs, for which a searchable index is constructed, and the searchable data service may then be queried to return lists of eIDs from the searchable index that satisfy the queries. These lists of eIDs may then be used to access the data entities stored on the backend data store. As mentioned, one embodiment may provide a Web service interface that provides one or more Web service calls through which the developers may add the eIDs and associated attributes, update the searchable index (e.g., by modifying, replacing or deleting eIDs and attributes in the searchable index), and query the searchable data service to obtain lists of eIDs.

0046Embodiments of the searchable data service may be used to provide searchable indexes to any type of data. Embodiments may be used, for example, to provide searchable indexes to data stored in databases, and to repositories of files of various particular or mixed types including, but not limited to, textual, digital image, and digital audio files. For example, the searchable data service may be used to provide a searchable index to a digital image repository. Through a Web service interface to the searchable data service, clients on the Internet may open an account, store digital images, and provide indexing information for the digital images.

0047In one embodiment, an implementation of the searchable data service may provide the data store as well as a searchable index to the data store. In one embodiment, through a Web service or other interface to the searchable data service, clients may store entities to a data store and provide the eIDs and associated attributes for the entities, which are used to create the searchable index for the data store. The clients may then query the searchable index via the interface to the searchable data service, and use the results of the queries to access the data store via the interface to the searchable data service.

0048Note that, while embodiments of the searchable data service are generally referred to herein as providing a searchable index to a backend data store, embodiments may be used in applications where there may be no backend data store. In these applications, the attributes stored as {name, value} pairs in the searchable index are the data. In these applications, there are no “entities” stored in a backend data store; in a sense, the entities are the attributes in the searchable index. In one embodiment, through a Web service or other interface to the searchable data service, clients may provide their data as {name, value} pairs, which are used to create the searchable index. The clients may then query the searchable index via the interface to the searchable data service to obtain desired data. Examples of applications for which the searchable data service may be used and in which there is no backend data store may include, but are not limited to, product catalogs and phone directories.

0049Embodiments of the searchable data service may include mechanisms that enable the searchable data service to scale easily, and to provide redundancy, reliability, and high availability of the searchable indexes without requiring any knowledge or additional effort by a developer leveraging the searchable data service to provide a search frontend to a backend data store. These mechanisms may include, but are not limited to, a mechanism for building the searchable indexes, a mechanism for partitioning the searchable indexes, a mechanism for replicating the searchable indexes, a mechanism for handling the failure of nodes within the searchable data service, and a mechanism for the automated monitoring and control of nodes within the searchable data service.

0050Some embodiments of the searchable data service may be implemented as a distributed system with a Web services frontend, with various nodes in the system configured to perform various functions. For example, in one embodiment, there may be one or more coordinator nodes that coordinate the routing of requests from client systems to one or more other appropriate nodes, for example routing clients' query (read) requests received via a Web service interface to one or more appropriate query nodes and clients' storage (write) requests received via a Web service interface to one or more appropriate storage nodes; one or more query nodes that handle the processing of query requests including the routing of query requests to appropriate storage nodes, and one or more storage nodes that manage the storage of eIDs and associated attributes in response to storage requests and the retrieval of stored eIDs in response to query requests received from the query nodes.

0051The various nodes in the distributed system may communicatively cooperate to ensure that the searchable indexes are scalable, consistent, available, and durable. In one embodiment, communications among nodes in a searchable data service implementation may be facilitated at least in part through a gossip protocol. In one embodiment, communications among nodes in a searchable data service implementation may be facilitated at least in part through an anti-entropy protocol. In one embodiment, communications among nodes in a searchable data service implementation may be facilitated at least in part through a gossip protocol and an anti-entropy protocol. In one embodiment, two or more nodes in a searchable data service implementation may participate in groups according to a group communications protocol that uses the gossip protocol and/or the anti-entropy protocol to facilitate the cooperative performance of various functions among the nodes within the group, such as the cooperative movement of partitions or the cooperative replication of partitions within groups of storage nodes.

0052In one embodiment, a searchable index (also referred to as a domain, or bucket) created by a subscriber may be initially created as one partition, and that partition (and any subsequently created partitions) may be repartitioned on a storage node, and one of the resulting new partitions may then be cooperatively moved to another storage node within a data center or in another data center, to allow the searchable index to grow beyond the storage limits of one node or even one data center. Partitioning may also be used to improve performance by allowing client storage (write) requests to be distributed among two or more nodes.

0053Partitions of a domain may be replicated to other storage nodes, within a data center or across data centers, to provide redundancy of data, which may help to ensure that the searchable index remains available and is durable. Replication may also be used to improve performance by allowing client query (read) requests to be distributed among two or more nodes. In one embodiment, replication may be performed using anti-entropy to copy the partition from one storage node to another storage node, and then using the gossip protocol to bring the replicated partition up-to-date. The storage nodes that store replicas of a particular partition may cooperatively participate in a replication group, and group communications may be used within the group to propagate updates to the partition. In one embodiment, writes to a replicated partition may initially be directly applied on one or more storage nodes within the replication group, and then propagated to the other storage nodes within the replication group using the gossip protocol.

0054Group communications may be used to monitor the health and status of various nodes, components, and other resources within the searchable data service implementation; and may enable the automatic addition of new resources to replace existing resources that fail or become unavailable for any reason. For example, group communications may be used to automatically recruit a new storage node into a storage node group (e.g., a replication group) if one of the existing storage nodes goes offline.

0055Embodiments of the searchable data service may use key-value pair storage to store the eIDs and associated other attributes (expressed as {name, value} pairs) of entities in an eID store. Note that the eIDs may be considered as one of the attributes of the associated entities, and may be stored in the eID store as a key-value pair. In one embodiment, the key-value pair storage may be implemented according to an associative dictionary database architecture to store the eIDs and associated other attributes. The associative dictionaries used to store attributes in embodiments may be capable of high throughput, especially when reading, at relatively little CPU cost. The associative dictionaries are simple, which may aid in maintaining reliability, in ease of use, and in flexibility. Further, the associative dictionaries may be inexpensive when compared to alternatives like relational databases.

0056In one embodiment, the eID store may be implemented in accordance with a Berkeley Database. The Berkeley Database is an open source embedded database system that uses key-value pairs, and that may be used to create indexes to tables and other data structures. Unlike relational databases, a Berkeley Database does not support SQL queries. All queries and data analyses are instead performed by the application through a Berkeley Database application programming interface (API). Note that other embodiments may use other database structures for the eID store.

0057Embodiments of the searchable data service may make indexed search available on the Web using Web services. Embodiments may make it easy for developers to add search capabilities to their applications. Developers of applications that need to access data objects stored in a data store may need or desired to enable the application to retrieve data objects based on one of several attributes or a combination of attributes. By combining associative dictionaries with search indexes, and making indexed search available through a Web service interface, embodiments of the searchable data service may allow developers to leverage the searchable data service to inexpensively and easily implement a searchable index frontend for such applications that provides the speed and query power needed or desired for many such applications to retrieve locators for data objects stored in data stores based on one attribute or a combination of attributes.

0058Note that the implementation of the searchable data service, including the various mechanisms, subsystems, and components of the searchable data service described herein, may be transparent to the client/developer. The client and/or developer may only need to be aware of a minimal, externally exposed interface to the searchable data service, which may be provided through a Web service interface, that allows the client/developer to build and update a searchable index (domain) and to query the searchable data service for lists of eIDs from the searchable index.

0059<figref idref="DRAWINGS">FIG. 2</figref> illustrates the relationship and dataflow between a client and the searchable data service, according to one embodiment. A data store <b>332</b> may include data entities that are accessible via locators. A searchable data service <b>340</b> implementation may expose an API via a Web service interface <b>350</b>. A client <b>330</b> may have access to the functionalities of the searchable data service <b>340</b> via the Web service interface. A developer of an application (e.g., client <b>330</b>) may leverage the searchable data service <b>340</b>, via the calls provided by the Web service interface <b>350</b>, to provide a frontend search service to the data store <b>332</b>.

0060The client <b>330</b> may provide locators (eIDs) and associated attributes (which may be described by {name, value} pairs) for at least some of the entities in data store <b>332</b> to the searchable data service <b>340</b> via Web service interface <b>350</b>. Searchable data service <b>340</b> may store the eIDs and associated attributes in buckets as described above, and may build indexes for the attributes, to generate searchable index <b>342</b>. Client <b>330</b> may then query the searchable data service <b>340</b> via Web service interface <b>350</b>. Searchable data service <b>340</b> executes the queries against the searchable index <b>342</b> to locate eIDs that satisfy the queries. Searchable data service <b>340</b> may return query results including lists of eIDs that satisfy the queries to the client <b>330</b>.

0061The following are definitions for some terms used herein to describe aspects of embodiments of the searchable data service: <ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0062"> Entity: An entity refers to any data object or entity, which may be stored in a data store <b>332</b> of some type, to which the developer wants to associate attributes. </li><li id="ul0001-0002" num="0063"> Entity identifier (eID): a string (e.g., a UTF-8 encoded string) that a developer may use to uniquely identify an entity to their application. An eID may also be referred to as a locator. In some use cases, an eID may be used to locate a blob-like entity. In one embodiment, the searchable data service may be opaque to the storage solution used by the developer. In one embodiment, UTF-8 encoding may be used for eIDs to support features that require ordering of eIDs. Note that, in one embodiment, an eID may be an arbitrary sequence of bytes (but unique within the domain or bucket). </li><li id="ul0001-0003" num="0064"> Attribute: refers to {name, value} pairs, which may be expressed as strings, which are associated with eIDs, and based on which the eIDs may be indexed and queried. In one embodiment, attributes may be UTF-8 encoded strings so that the attributes may readily be used in UTF-8 encoded query expression strings. </li><li id="ul0001-0004" num="0065"> Index: Each of the attributes associated with an eID may have or may be given an index that may be queried to retrieve the list of eIDs that satisfy the query expression. </li><li id="ul0001-0005" num="0066"> Sequence ID: A searchable data service-generated unique identifier that acknowledges receipt of an update request and allows the status of the update to be tracked. In one embodiment, the sequence ID may be used in ordering and in maintaining the consistency of update requests; a request with a higher sequence ID globally supercedes a request with a lower sequence ID. Note that, in one embodiment, the sequence ID may not be exposed to the client. </li><li id="ul0001-0006" num="0067"> Client (e.g., client <b>330</b> in <figref idref="DRAWINGS">FIG. 2</figref>): The term client may be used to represent any application, script, piece of software, etc., developed by a searchable data service subscriber who would like to use the searchable data service system. </li><li id="ul0001-0007" num="0068"> Subscriber: A searchable data service subscriber may be uniquely identified by a subscriber identifier for billing, metering, and possibly other purposes. Each searchable data service subscriber may have more than one client accessing their data in searchable data service using the same subscriber identifier. The subscriber identifier may be used within the searchable data service to locate the subscriber's eID data stored in the searchable data service. A subscriber may be the owner of one or more buckets. A subscriber may also be referred to as a customer. </li><li id="ul0001-0008" num="0069"> Searchable data service request: refers to a call (including the data) that the client sends to the searchable data service, via the Web service interface, to perform one or more of the searchable data service operations described herein. </li><li id="ul0001-0009" num="0070"> Searchable data service response: refers to a response that the searchable data service sends back to the client once it has processed the searchable data service request sent by the client. </li><li id="ul0001-0010" num="0071"> Bucket: refers to a group of searchable data service objects that the subscriber may wish to keep together for semantic or other reasons. A query is applied across one bucket. A bucket may also be referred to as a domain or as a searchable index. Each bucket may be identified by a bucket identifier. In one embodiment, each subscriber identifier may be associated with one or more bucket identifiers, but a bucket identifier may be associated with one and only one subscriber identifier. </li></ul>

0072The following illustrates the relationship between a subscriber, a bucket, and an entity identifier (eID): <ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0073"> subscriber -> bucket -> eID </li></ul>

0074In one embodiment, the searchable data service logically maintains an eID->attributes table for every subscriber bucket. The following is a representation of an exemplary eID->attributes table: <tables id="TABLE-US-00001" num="1"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="1" colwidth="70PT" align="center" /><colspec colname="2" colwidth="147PT" align="left" /><thead><row><entry /></row><row><entry namest="1" nameend="2" align="center" rowsep="1" /></row><row><entry>eID</entry><entry>Attributes</entry></row><row><entry namest="1" nameend="2" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry>k1</entry><entry>{{name, value}}, {{name, value}}, . . .</entry></row><row><entry>k2</entry><entry>{{name, value}}, {{name, value}}, . . .</entry></row><row><entry>k3</entry><entry>{{name, value}}, {{name, value}}, . . .</entry></row><row><entry>. . .</entry><entry>. . .</entry></row><row><entry namest="1" nameend="2" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0075In one embodiment, every eID is unique in the table (within a bucket); an eID may thus be viewed as a subscriber-provided entity key. In one embodiment, an eID may be composed of printable characters.

0076Concerning the relationship between attributes and {name, value} pairs, attributes may typically be represented by one {name, value} pair. However, in one embodiment, it is possible to have more than one {name, value} pair with the same name on any row in the table above, indicating a multi-valued attribute of that name. For example, the following exemplary row from an eID->Attributes table illustrates that the keywords attribute is multi-valued for the particular URL specified as the eID. <tables id="TABLE-US-00002" num="2"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="3"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="42PT" align="left" /><colspec colname="2" colwidth="161PT" align="left" /><thead><row><entry /><entry /></row><row><entry /><entry namest="OFFSET" nameend="2" align="center" rowsep="1" /></row><row><entry /><entry>eID</entry><entry>Attributes</entry></row><row><entry /><entry namest="OFFSET" nameend="2" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry /><entry><url></entry><entry>(name = “keywords”, value = “xxx”), (name =</entry></row><row><entry /><entry /><entry>“keywords”, value = “yyy”), . . .</entry></row><row><entry /><entry namest="OFFSET" nameend="2" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0077In one embodiment, all values in {name, value} pairs are expressed as strings. To have comparison operators for strings return the same truth-value as numbers, the numbers may be zero-padded. For example, “21”>“100” is true when “>” is comparing strings, but false when it is comparing numbers; however, “021” and “100” have the same truth-value when compared as strings or numbers. In one embodiment, a format such as ISO 8601 may be used to allow date-time values to be compared correctly as strings.

0078In one embodiment, each row of an eID->Attributes table may be considered a searchable data service object. A searchable data service object may be expressed as: <ul id="ul0003" list-style="none"><li id="ul0003-0001" num="0079"> Subscriber -> Bucket -> eID -> {Attributes list}</li></ul>

0080Searchable data service objects may be created when a subscriber wishes to build indexes that may be used to search for entities in a data store used by a client application and identified by an entity identifier (eID). When creating a searchable data service object, the subscriber may provide at least the following inputs: <ul id="ul0004" list-style="none"><li id="ul0004-0001" num="0081"> Subscriber ID </li><li id="ul0004-0002" num="0082"> Bucket identifier—identifies the domain </li><li id="ul0004-0003" num="0083"> eID </li><li id="ul0004-0004" num="0084"> Attributes list—a list of {name, value} pairs associated with the entity </li></ul>

0085In one embodiment, the searchable data service may automatically provide one or more other attributes, also expressed as {name, value} pairs, for a searchable data service object. These other attributes may be indexed and searched in addition to the list of attributes provided by the subscriber. These attributes may be referred to as basic attributes. In one embodiment, all searchable data service objects in all domains and for all subscribers may include these basic attributes. In another embodiment, one or more of these basic attributes may be optional. Basic attributes may include one or more of, but are not limited to: <ul id="ul0005" list-style="none"><li id="ul0005-0001" num="0086"> Creation time/date—a timestamp that indicates when the searchable data service object was created. </li><li id="ul0005-0002" num="0087"> Last modified time/date—a timestamp that indicates when the searchable data service object was last modified. Initially, may be the same as the creation time/date. </li><li id="ul0005-0003" num="0088"> Last accessed time/date—a timestamp that indicates when the searchable data service object was last accessed. </li><li id="ul0005-0004" num="0089"> Created by—indicates a particular user/client that created this searchable data service object. </li><li id="ul0005-0005" num="0090"> Last modified by—indicates a particular user/client that last modified this searchable data service object. </li><li id="ul0005-0006" num="0091"> Size—indicates a size (e.g., in bytes) of this searchable data service object. </li><li id="ul0005-0007" num="0092"> Access rights—indicates access rights for this searchable data service object. </li></ul>

0093A searchable data service object may be considered successfully created when all attributes specified by the subscriber, and the basic attributes, are indexed, and the eID is persistently stored. When a searchable data service object is not created successfully, an error code and message may be returned to the subscriber that may indicate a reason or reasons why an object could not be created.

0094In one embodiment, a subscriber may read a searchable data service object and the basic attributes associated with the object by the searchable data service. In one embodiment, a searchable data service object may be read from the searchable data service by specifying the subscriber identifier, bucket identifier, and eID of the searchable data service object.

0095In one embodiment, a subscriber may update searchable data service objects by providing the subscriber identifier, bucket identifier, and eID of the searchable data service object to be updated, along with update information. In one embodiment, a subscriber may add or delete eIDs, add or delete attributes for an eID, and modify the values associated with existing attributes. In one embodiment, the subscriber may not be allowed to add, delete, or modify at least some of the basic attributes. However, when the subscriber modifies a searchable data service object, one or more of the basic attributes associated with object modification may be updated.

0096In one embodiment, a searchable data service object may be considered successfully updated only when all the eIDs and attributes that the subscriber wishes to modify as specified in a request message have been updated, including the indexes associated with the attributes. In one embodiment, partial updates may not be allowed. For example, if a request specifies multiple attributes that need to be modified, and one of the modifications cannot be performed, the entire update request may be failed, with none of the modifications performed. When a searchable data service object is not updated successfully, an error code and message may be returned to the subscriber that may indicate a reason or reasons why the object could not be updated.

0097In one embodiment, a subscriber may delete existing searchable data service objects from a domain by providing the subscriber identifier, bucket identifier, and eID of the object(s) to be deleted. In one embodiment, a searchable data service object is successfully deleted only when there is no longer a guarantee that the object can be accessed with the eID associated with the object and when the object is no longer searchable. In one embodiment, after the deletion of a searchable data service object, there might be a period when the eID may still be used to access the object. Additionally it is possible that the object may be searchable for a period. If a searchable data service object and its associated indexes cannot be deleted, the delete request fails, and the subscriber may be notified of the failure via an error code and message. In one embodiment, once a searchable data service object is deleted from a domain, the eID may be reused by the subscriber within the domain.

0098In one embodiment, a subscriber may request listings of the subscriber's domains (buckets), indexed attributes, searchable data service objects, and eIDs. Along with the searchable data service objects and the subscriber-provided attributes, subscribers may also have access to the basic attributes provided by the searchable data service when listing searchable data service objects. In one embodiment, a subscriber may perform one or more of, but not limited to, the following list operations: <ul id="ul0006" list-style="none"><li id="ul0006-0001" num="0099"> List all the searchable data service objects and/or eIDs that match a specified prefix. </li><li id="ul0006-0002" num="0100"> List all the domains (buckets) associated with the subscriber and identified by a unique subscriber identifier. </li><li id="ul0006-0003" num="0101"> List all attributes indexed under a domain (in a bucket). </li><li id="ul0006-0004" num="0102"> List all searchable data service objects and/or eIDs under a domain. </li><li id="ul0006-0005" num="0103"> List all attributes indexed by a specified client. </li><li id="ul0006-0006" num="0104"> List all searchable data service objects and/or eIDs for a customer across all domains. </li><li id="ul0006-0007" num="0105"> List all searchable data service objects and/or eIDs that have a specified attribute. </li></ul>

0106Given that a large number of domains, attributes, searchable data service objects or locators may be returned in response to a list request, the searchable data service may paginate list results. The client may retrieve the list in pieces (pages) via multiple requests.

0107In one embodiment, a subscriber may search the searchable data service objects and eIDs via a query request exposed via the Web service interface. Subscribers may perform queries on one or more of the attributes of searchable data service objects within a single domain (bucket) to obtain a list of eIDs that satisfy the query expression. In one embodiment, the searchable data service may support one or more of, but not limited to, the following operators on attributes in the query expressions. These operators may be used in combination: <ul id="ul0007" list-style="none"><li id="ul0007-0001" num="0108"> Boolean (e.g., AND, OR, NOT) </li><li id="ul0007-0002" num="0109"> Arithmetic (e.g., <, >, =, !=, <=, >=, <>) </li><li id="ul0007-0003" num="0110"> Contains (an attribute contains a specified string) </li><li id="ul0007-0004" num="0111"> Starts with (an attribute starts with a specified string) </li></ul>

0112A query operation may return the eIDs of the searchable data service objects that satisfy the query expression. In one embodiment, the complete searchable data service objects may be optionally returned. In one embodiment, the results of a query may be sorted in either ascending or descending order based on a sort specification provided by the subscriber in the query message. Given that a large number of eIDs may be returned in response to a query, the searchable data service may paginate query results. The client may then retrieve the list of eIDs in pieces (pages) over multiple requests. In one embodiment, the client may provide a page length specification in the query message that specifies the number of entries (eIDs) on a page.

0113In one embodiment, a subscriber may delete a domain (bucket), if desired. A domain may be considered successfully deleted only if all of the indexes associated with attributes in the domain and searchable data service objects in the domain are deleted. If the searchable data service objects and their associated indexes in the domain cannot be deleted, the delete request fails, and the subscriber may be notified of the failure via an error code and message.

0114In one embodiment, a subscriber may delete an index within a domain. An index may be considered successfully deleted if all the attributes within the index are successfully deleted. If the index in the domain cannot be deleted, the delete request fails, and the subscriber may be notified of the failure via an error code and message.

0115One embodiment of the searchable data service may provide a mechanism whereby a subscriber may submit at least some operations to be performed on a bucket in batch mode. A batch mode mechanism may be used, for example, by subscribers that may have large datasets that they would like to upload to the searchable data service. An exemplary batch mode mechanism may, for example, allow a subscriber to submit a file in which each line represents one operation, for example an operation to add a searchable data service object. An exemplary line from such a file may include, but is not limited to: <ul id="ul0008" list-style="none"><li id="ul0008-0001" num="0116"> Bucket identifier—identifies the domain </li><li id="ul0008-0002" num="0117"> Operation—indicates the operation to be performed. For example, ADD, DELETE, or MODIFY. </li><li id="ul0008-0003" num="0118"> ID </li><li id="ul0008-0004" num="0119"> Attributes list <br /> Exemplary Searchable Data Service API </li></ul>

0120This section describes an exemplary API for a searchable data service <b>340</b> that may be exposed to developers and clients as a Web service via a Web service interface <b>350</b> according to one embodiment. In one embodiment, the API may be provided to developers and clients through a Web services platform via Fully REpresentational State Transfer (REST) and/or Simple Object Access Protocol (SOAP) over HTTP/HTTPS. Other embodiments may use other protocols. The provided Web service interface <b>350</b> may be application-agnostic.

0121The following describes exemplary requests that may be made by a client to the searchable data service via the Web service interface <b>350</b> according to one embodiment. Note that these descriptions are exemplary, and are not intended to be limiting. Other embodiments may include other requests, and/or may include variations of the described requests.

0122In one embodiment, the following types of client operations may be allowed by the searchable data service. These operations may be exposed to the client via the Web service interface: <ul id="ul0009" list-style="none"><li id="ul0009-0001" num="0123"> Update: An operation to update the eID-attributes bucket. E.g., add, replace, and delete operations. </li><li id="ul0009-0002" num="0124"> List-Attributes: Given an eID and a bucket identifier, this operation lists the eID's attributes. This may be visualized as going from left to right in the table above—for example, if given “k<b>1</b>” as an argument, all of the {name, value} pairs on the right of “k<b>1</b>” are returned. </li><li id="ul0009-0003" num="0125"> Query-eID Given a query expression, return all eIDs from a bucket that satisfy that expression. </li></ul>

0126This may be visualized as going from right to left in the table above. In one embodiment, a query expression is a collection of predicates combined using Boolean operators (e.g., NOT, AND, OR). A predicate expresses a condition that must hold true for the name and/or value fields of the attribute list.

0000Update Operations

0127These searchable data service operations may be invoked by the client via the Web service interface to update the eID-attributes bucket of a subscriber.

0128In one embodiment, a replace operation may create an attribute if the attribute does not exist. Subsequent invocations of the replace operation may revise (update) the value, and may ensure that there is only one value for that attribute at any given time. Updates of unique valued attributes should use this operation. In one embodiment, a client request to invoke the replace operation may include one or more of, but is not limited to, the following information: <ul id="ul0010" list-style="none"><li id="ul0010-0001" num="0129"> Bucket identifier: A string that identifies a bucket of the subscriber. If a bucket does not exist, one may be created. </li><li id="ul0010-0002" num="0130"> eID: A string that may be used by the client to locate entities in a data store. </li><li id="ul0010-0003" num="0131"> Name: A string that represents the name of an attribute. </li><li id="ul0010-0004" num="0132"> Value: A string that represents the value of an attribute. </li><li id="ul0010-0005" num="0133"> Subscriber identifier: Identifies a searchable data service subscriber, and may be used to bill and authenticate the subscriber. In one embodiment, credentials for the subscriber may also be included. </li></ul>

0134In one embodiment, an add operation creates an attribute if the attribute does not exist. A subsequent invocation of the add operation with the same name and a different value may add another value to the attribute, and thus allows creation of multi-valued attributes. In one embodiment, a client request to invoke the add operation may include one or more of, but is not limited to, the following information: <ul id="ul0011" list-style="none"><li id="ul0011-0001" num="0135"> Bucket identifier: A string that identifies a bucket of the subscriber. If the bucket does not exist, one may be created. </li><li id="ul0011-0002" num="0136"> eID: A string that may be used by the client to locate entities in a data store. </li><li id="ul0011-0003" num="0137"> Name: A string that represents the name of an attribute. </li><li id="ul0011-0004" num="0138"> Value: A string that represents the value of an attribute. </li><li id="ul0011-0005" num="0139"> Subscriber identifier: Identifies a searchable data service subscriber, and may be used to bill and authenticate the subscriber. In one embodiment, credentials for the subscriber may also be included. </li></ul>

0140In one embodiment, a delete operation may invoke one of the following, depending on whether an optional name and/or a {name, value} pair is specified: <ul id="ul0012" list-style="none"><li id="ul0012-0001" num="0141"> Without either the name or value specified, the delete operation may delete all attributes associated with the given eID. In one embodiment, the eID becomes a candidate for garbage collection after a time interval if no new attributes are introduced with add or replace operations. </li></ul>

0142In one embodiment, buckets with no eIDs may become candidates for garbage collection. In one embodiment, attributes may be marked as deleted and no active garbage collection is performed. <ul id="ul0013" list-style="none"><li id="ul0013-0001" num="0143"> With just the name but no value specified, the delete operation may delete the attribute with that name and associated with the given eID. The attribute may either have a unique value or be multi-valued. </li><li id="ul0013-0002" num="0144"> With both the name and value specified, the delete operation may delete that {name, value} pair associated with the given eID. This allows the client to delete one particular value in a multi-valued attribute. </li></ul>

0145In one embodiment, a client request to invoke the delete operation may include one or more of, but is not limited to, the following information: <ul id="ul0014" list-style="none"><li id="ul0014-0001" num="0146"> Bucket identifier: A string that identifies a bucket of the subscriber. </li><li id="ul0014-0002" num="0147"> eID: A string that may be used by the client to locate entities in a data store. </li><li id="ul0014-0003" num="0148"> Name: A string that represents the name of an attribute. </li><li id="ul0014-0004" num="0149"> Value: A string that represents the value of an attribute. </li><li id="ul0014-0005" num="0150"> Subscriber identifier: Identifies a searchable data service subscriber, and may be used to bill and authenticate the subscriber. In one embodiment, credentials for the subscriber may also be included. </li></ul>

0151Each of the eID-attributes bucket update operations described above may generate an update response to the client which includes update results. In one embodiment, the update response may be forwarded to the client via the Web service interface to the searchable data service. In one embodiment, an update response may be sent to the client to inform the client of the results of the update both for update operations that were successful to notify the client that the update operation was successful, and in cases where the update operation could not be performed for some reason to notify the client that the update operation failed. In one embodiment, each of the update operations described above may use a similar response structure. The following illustrates information that may be included in an exemplary response to an update operation request. Note that this is exemplary and not intended to be limiting: <ul id="ul0015" list-style="none"><li id="ul0015-0001" num="0152"> Status: Either “OK” or “ERROR” If the update is correctly formed and can be applied, the status is OK; otherwise, the response may explain the problem(s) in the error message. </li><li id="ul0015-0002" num="0153"> Error message: information that further explains any problem(s) encountered with the update operation request. E.g., “Request ill-formed.” <br /> Batched Update Requests </li></ul>

0154One embodiment may provide a mechanism via which update requests may be batched, or submitted as a batch operation. A batched update request may include a sequence of two or more update requests as described above, and a response to the batched update request may contain a sequence of update statuses corresponding to the batched update requests. In one embodiment, to sequentially process the update operations specified in a batched update request in real-time, there may be a limit on the number of update operations that may be submitted in a single batch update request. Alternatively, the updates in a batched update request may be performed asynchronously.

0000List-Attribute Operation

0155One embodiment may provide a list-attributes operation that may be invoked by a client via the Web service interface. A list-attributes operation may return a list of attributes associated with a specified eID. The following illustrates information that may be included in an exemplary list-attributes operation request. Note that this is exemplary and not intended to be limiting: <ul id="ul0016" list-style="none"><li id="ul0016-0001" num="0156"> Bucket identifier: A string that identifies a bucket of the subscriber. </li><li id="ul0016-0002" num="0157"> eID: A string that may be used by the client to locate entities in a data store. </li><li id="ul0016-0003" num="0158"> Filter expression: A string expression that may be used to filter the attributes returned for the eID. If no filter expression is specified, all the attributes associated with the eID are returned. The syntax of the filter follows the one used for “Query-eID” as described below. This parameter may be optional. </li><li id="ul0016-0004" num="0159"> Subscriber identifier: Identifies a searchable data service subscriber, and may be used to bill and authenticate the subscriber. In one embodiment, credentials for the subscriber may also be included. </li></ul>

0160The following illustrates information that may be included in an exemplary list-attributes operation response to the client: <ul id="ul0017" list-style="none"><li id="ul0017-0001" num="0161"> Attribute list: List of {name, value} pairs that match the filter expression, if any. All attributes for the specified eID may be returned if there is no filter expression given in the request. If there is no error, this is the expected return. </li><li id="ul0017-0002" num="0162"> Error message: Information that explains any problem(s) encountered with the list-attributes operation request. E.g., “Unknown Entity Identifier”, “Unknown Bucket”, or “Filter expression has incorrect syntax”. <br /> Query-eID Operation </li></ul>

0163One embodiment may provide a query-eID operation, or simply query operation, that may be invoked by a client via the Web service interface. The query-eID operation returns a list of eIDs that match the criteria specified through a query expression. A query expression is a string that may follow a set of rules given below in the section titled <i>Query Syntax and Search Expressions</i>. Some embodiments of the searchable data service, however, may accept unnormalized search expressions with implicit syntax and reduce the statements to the canonical form using one or more normalization rules (see the section titled <i>Unnormalized Search Expressions</i>). Note that a query-eID operation request may be referred to herein as a query, a query request, or a query node request.

0164The following illustrates information that may be included in an exemplary query-eID operation request. Note that this is not intended to be limiting: <ul id="ul0018" list-style="none"><li id="ul0018-0001" num="0165"> Bucket identifier: A string that identifies a bucket of the subscriber. </li><li id="ul0018-0002" num="0166"> Query expression: A string expression, according to which a list of eIDs may be located and returned. </li><li id="ul0018-0003" num="0167"> MoreToken: An opaque object (e.g., a cookie) that may have been returned to the client in a previous query-eID operation request. If a token is returned from an earlier query-eID operation, the token may be provided in a subsequent query-eID operation request to request that the next page in a list of eIDs located in response to the previous query-eID operation request be returned. This is an optional parameter. </li><li id="ul0018-0004" num="0168"> Subscriber identifier: Identifies a searchable data service subscriber, and may be used to bill and authenticate the subscriber. In one embodiment, credentials for the subscriber may also be included. </li></ul>

0169The following illustrates information that may be included in an exemplary query-eID operation response to the client. <ul id="ul0019" list-style="none"><li id="ul0019-0001" num="0170"> Entity identifier list: A list of eIDs that match the search criteria specified in the query request. </li></ul>

0171This is the expected return unless there is an error, in which one or more error messages may be returned. <ul id="ul0020" list-style="none"><li id="ul0020-0001" num="0172"> MoreToken: A string; in one embodiment, MoreToken is opaque to the client. If the list of eIDs to satisfy a query request is too large to be returned in one response, the list may be returned in “pages”. The MoreToken “cookie” may indicate the “last page seen”. The More Token cookie may be included in a subsequent query request to retrieve the next page of eIDs. </li><li id="ul0020-0002" num="0173"> Error message: Information that explains any problem(s) encountered with the query-eID operation request. E.g., “Unknown bucket”, “Query expression does not have right syntax”, or “Invalid MoreToken”. <br /> Searchable Data Service Architecture </li></ul>

0174The previous sections described an exemplary Web services API exposed to developers/clients for embodiments of the searchable data service. In the following sections, an exemplary architecture for implementations of a searchable data service, and various subsystems and components that may be included in an implementation of a searchable data service, are described.

0175<figref idref="DRAWINGS">FIG. 3</figref> illustrates an exemplary high-level functional architecture for a searchable data service, according to one embodiment. In this embodiment, the searchable data service may include one or more of, but is not limited to, the following major components and subsystems: a Web services platform <b>200</b>, a request router <b>202</b>, a query subsystem <b>204</b>, and a storage subsystem <b>206</b>. Note that other embodiments may have other components and/or subsystems, or combinations or numbers of components and/or subsystems, at this architectural level.

0176The Web services platform <b>200</b> may include one or more Web servers that serve as a front-end to the searchable data service. The Web services platform <b>200</b> may perform one or more of, but is not limited to, the following functions: <ul id="ul0021" list-style="none"><li id="ul0021-0001" num="0177"> Through request-interceptors, the Web servers may interact with one or more other services for the metering, billing, authentication, and access rights to the searchable data service. </li><li id="ul0021-0002" num="0178"> The Web servers may provide one or more Fully REpresentational State Transfer (REST) and/or Simple Object Access Protocol (SOAP) APIs that are exposed to developers and clients for submitting data to or retrieving data from the searchable data service. Note that other embodiments may use one or more other protocols or combinations of protocols. These APIs allow the receipt and storage of entity locators (eIDs) and attributes associated with the entities in an entity ID (eID) store. Indexes for the attributes may be built from the eID Store. In one embodiment, the APIs may provide one or more of, but are not limited to, the following API calls dealing with eIDs and attributes (which may be referred to as storage node requests or storage requests): <ul id="ul0022" list-style="none"><li id="ul0022-0001" num="0179"> add—add an attribute (a {name, value} pair) for an entity. Used primarily for attributes with multiple values, such as an attribute like “keywords”, that may have two or more values. </li><li id="ul0022-0002" num="0180"> delete—remove an attribute. </li><li id="ul0022-0003" num="0181"> replace—replace an existing attribute. May primarily be used with attributes that have a single value. </li><li id="ul0022-0004" num="0182"> list attributes—list all {name, value} pairs for an entity. </li></ul></li><li id="ul0021-0003" num="0183"> The Web servers may provide one or more REST and/or SOAP APIs for submitting query requests to the searchable data service. Note that other embodiments may use one or more other protocols or combinations of protocols. In one embodiment, there is one query API call (query-eID). Query requests may also be referred to as query node requests. </li></ul>

0184The request router <b>202</b> may perform one or more of, but is not limited to, the following functions: <ul id="ul0023" list-style="none"><li id="ul0023-0001" num="0185"> The request router <b>202</b> may receive a service request from the Web services platform <b>200</b> and determine whether the service request is a storage node request (e.g., a request to add, delete or replace one or more eIDs and associated attributes) or a query node request (a request to retrieve one or more stored eIDs and/or associated attributes). </li><li id="ul0023-0002" num="0186"> If the service request is a storage node request, request router <b>202</b> queries a storage node locator to map the eID and bucket specified in the request to an appropriate storage node. In one embodiment, searchable data service indexing data may be segregated into buckets. Buckets define the limits of data that may be considered in a single query. </li><li id="ul0023-0003" num="0187"> If the service request is a query node request, request router <b>202</b> queries a query node locator to map the bucket and query expression to an appropriate query node. The request router <b>202</b> routes the service request to the appropriate node, collects results, and sends the results back to the Web services platform <b>200</b>. </li></ul>

0188The query subsystem <b>204</b> (which may also be referred to as a query service) may perform one or more of, but is not limited to, the following functions: <ul id="ul0024" list-style="none"><li id="ul0024-0001" num="0189"> Processes queries. </li><li id="ul0024-0002" num="0190"> Services queries from query caches maintained by the query subsystem <b>204</b>, if possible. Sends queries not satisfied from a query cache to one or more storage nodes on storage subsystem <b>206</b> for execution. For a small domain (bucket), a query typically may run on a single storage node. Larger buckets may be partitioned across multiple storage nodes, requiring queries to be executed on one storage node for each partition. Similar to the request router <b>202</b>, the query subsystem <b>204</b> may use a local instance of a storage node locator to find appropriate storage nodes. </li><li id="ul0024-0003" num="0191"> Aggregates query results received from two or more storage nodes, and sorts query results, if necessary. </li><li id="ul0024-0004" num="0192"> Returns the query results to the querying client via the Web service interface provided by the Web services platform <b>200</b>. In one embodiment, paginates the results if necessary. </li></ul>

0193The storage subsystem <b>206</b> may include one or more storage nodes. The storage nodes may be located in one or more data centers. Storage nodes may perform one or more of, but are not limited to, the following functions: <ul id="ul0025" list-style="none"><li id="ul0025-0001" num="0194"> On a storage node, a local eID store may serve as the authoritative store for eIDs and their attributes. </li><li id="ul0025-0002" num="0195"> Indexes may be built from the eID store that may index all attributes for eIDs on the local storage node. </li><li id="ul0025-0003" num="0196"> A local query processor may run queries against the local eID Store. </li><li id="ul0025-0004" num="0197"> An eID update service may apply storage node requests (add, replace, delete, etc.) to the local eID Store. </li><li id="ul0025-0005" num="0198"> A local partition manager may observe the use of local resources (disk space, CPU load, network bandwidth, etc.) for each storage node and manage the partitioning of buckets accordingly, and may cooperatively communicate with other storage nodes to move partitions. Partitions may be moved, for example, to maintain available storage space within a comfort zone on a storage node, and/or to provide load balancing. </li><li id="ul0025-0006" num="0199"> May cooperatively communicate with other storage nodes to replicate partitions across storage nodes, for example to provide redundancy of data. </li></ul>

0200In one embodiment, Web services platform <b>200</b> is the first point of contact when a client makes an API call to the searchable data service. Web services platform <b>200</b> may, for example, provide authentication, access control, logging, metering, and billing services for the searchable data service. Service requests from clients to the searchable data service API provided by Web services platform <b>200</b> may be broken into two categories: write requests to the storage subsystem <b>206</b>, which may be referred to herein as storage node requests or storage requests, and read requests to the query subsystem <b>204</b>, which may be referred to herein as query node requests, query requests or simply queries. Storage node requests may include, but are not limited to, requests to add, replace or delete locators (eIDs) and their associated attributes in a bucket in storage subsystem <b>206</b>. In addition, one embodiment may provide a construct API call that allows a client to request that a new domain (bucket) be created, to which eIDs and associated attributes may be added. Query node requests are queries to obtain lists of locators (eIDs) from a bucket in storage subsystem <b>206</b> according to a query expression in the query node request.

0201Web services platform <b>200</b> forwards incoming requests from clients to a request router <b>202</b>, which in one embodiment may be instantiated on a coordinator node of the searchable data service. In one embodiment, there may be two or more coordinator nodes and/or request routers <b>202</b> to distribute load and to provide redundancy by guarding against a single point of failure. Request router(s) <b>202</b> and one or more other associated components, which may reside on one or more coordinator nodes, may constitute a coordination subsystem or coordination service. Request router <b>202</b> examines an incoming service request to determine if the request is a storage node request or a query node request, determines an appropriate node (e.g., storage node or query node) to receive the request, and forwards the request to the determined node in the searchable data service implementation.

0202If the request is a storage node request, the client is requesting a write operation (e.g., add, delete, or replace) to indexing information stored in a bucket. Note that a storage node request may also be a list attributes request. Buckets define the limits of data that may be considered in a single query. In one embodiment, a bucket may be partitioned into one or more partitions, which may be stored on different storage nodes. Note, however, that a storage node may store more than one partition. Partitioning may allow clients of the searchable data service to store and maintain larger searchable indexes than can otherwise fit on a single storage node. Thus, distinct partitions of a bucket may reside on different storage nodes. Partitions may be replicated across storage nodes. Replication of partitions across storage nodes (and potentially across data centers) may provide redundancy of data, and thus durability, reliability, and availability of a client's searchable index, in the searchable data service. Partitioning and Replication mechanisms for the searchable data service are further described later in this document.

0203In one embodiment, if the request is a storage node request, request router <b>202</b> may query a local storage node locator to map a bucket and eID specified in the storage node request to a particular storage node in storage subsystem <b>206</b>. Request router <b>202</b> may also query the storage node locator to determine if the specified bucket has one partition or more than one partition. From the information received from the storage node locator, request router <b>202</b> determines a particular storage node in storage subsystem <b>206</b>, and then forwards the storage node request to the determined storage node. In the storage subsystem <b>206</b>, the storage node performs the operation specified in the storage node request on its local eID store. The storage node may then propagate the storage node request to other storage nodes in the storage subsystem <b>206</b> that store replicas of partitions of the bucket, if necessary.

0204If the request is a query node request, the client is requesting a read operation, or query on indexing information stored in a bucket. In one embodiment, if the request is a query node request, request router <b>202</b> may query a local query node locator to map the bucket and query expression specified by the request to an appropriate query node in query subsystem <b>204</b>. The request router <b>202</b> then forwards the query node request to the determined query node in query subsystem <b>204</b>.

0205On a query node in query subsystem <b>204</b>, some preprocessing (e.g., normalization) of a query request may be performed, for example to normalize a query expression specified in the query request. In one embodiment, a local query cache may be examined to determine if the query can be satisfied from the query cache. If the query can be satisfied from the local query cache, the query subsystem <b>204</b> returns query results from the query cache to the client via the Web services platform <b>200</b>. If the query cannot be satisfied from the query cache, a local instance of a storage node locator may be queried to locate one or more storage nodes in storage subsystem <b>206</b> to which the query is to be forwarded.

0206For a small domain (bucket), a query may run on a single storage node. Large domains (buckets) may be partitioned across multiple storage nodes, which may require queries to be executed on one storage node for each partition. The storage node(s) return results (lists of eIDs) to the query node in query subsystem <b>204</b>. In one embodiment, a query aggregator on the query node in the query subsystem <b>204</b> may aggregate results received from two or more storage nodes according to specifications in the query node request. Query subsystem <b>204</b> then returns the query results received from the storage node(s) to the client via the Web services platform <b>200</b>. In one embodiment, query subsystem <b>204</b> may paginate the query results as necessary or desired. On a query node, query results received from the storage subsystem <b>206</b> may be written to the local query cache.

0207As mentioned above, the request router <b>202</b> may query a local storage node locator and a local query node locator to locate storage nodes that are to receive storage node requests and query nodes that are to receive query node requests, respectively. In addition, a local storage node locator on a query node may be queried to locate storage nodes to receive query requests. The storage node locator tracks what storage nodes are in the storage subsystem <b>206</b>, and the query node locator tracks what query nodes are in the query subsystem <b>204</b>. Both node locators may use a table or database to record information on the respective nodes being tracked. In one embodiment, this table may be built in accordance with a Berkeley database. In one embodiment, when there is a change in the storage subsystem <b>206</b>, for example when a bucket is repartitioned, a partition is replicated, new storage nodes are added, new entries are added to a bucket, etc., the change may be communicated to the various node locators. Changes to the query subsystem <b>206</b>, such as additions or removals of query nodes, may be communicated to the query node locators. In one embodiment, one local node locator may be initially updated in response to a change, and the change may then be propagated from that node locator to other node locators on other nodes in accordance with the gossip protocol.

0208The searchable data service may include a communication mechanism among the various nodes and components that, for example, allows the storage and query node locators to monitor changes in the searchable data service implementation (e.g., added or removed nodes, replications, partitioning, writes to the storage subsystem <b>206</b>, etc.) and to thus update the information stored in their respective tables according to the communicated update information. In one embodiment, the communication mechanism may be implemented in accordance with a gossip, or epidemic, protocol. This communication mechanism may allow the propagation of changes on one node to all nodes and components of the searchable data service implementation that may require the information. In one embodiment, the communication mechanism provides weakly consistent updating; the communication mechanism propagates information, and so does not provide immediate updates to all nodes. However, the communication system may propagate updates sufficiently fast to maintain weak consistency among various nodes and components that may be tracking the information. In one embodiment, the communication mechanism propagates update information so that the communicated information does not overwhelm the communications bandwidth of the system. In one embodiment, this may be accomplished by piggybacking at least some update information on other inter-component or inter-node communications.

0209In one embodiment, an entity ID (eID) store in storage subsystem <b>206</b> may be implemented as a table of entity locators (eIDs) and, for each eID, a set of attributes, expressed as {name, value} pairs, that are associated with the entity. The eID store is the authoritative store of information in the searchable data service. When a client application of the searchable data service writes information into the searchable data service via a storage node request to the Web service interface provided by Web services platform <b>200</b>, the storage node request is routed to a particular storage node in the storage subsystem <b>206</b> by request router <b>202</b>, and on the storage node the information is written to the local eID store. Note that the information may be written to a particular bucket associated with the particular application, and that the bucket information may be provided in the storage node request. Thus, information for different client applications may be written into different buckets. In one embodiment, when a subscriber to the searchable data service initiates the creation of a searchable index for a particular application, the subscriber may provide a bucket identifier for that searchable index (bucket). When a request (e.g., a query) is made for that searchable index, the request references the bucket identifier of the searchable index. Note that the subscriber may be provided with a unique subscriber identifier that may be used to distinguish among multiple subscribers to the searchable data service. In one embodiment, the Web services platform may assign the subscriber identifier to the subscriber. A particular subscriber may have more than one searchable index, each assigned a bucket and given a bucket identifier. Thus, a particular subscriber identifier and a particular bucket identifier specify a domain in the searchable data service. Note that a bucket may be distributed across two or more local eID stores on two or more different storage nodes. A particular storage node eID store to which a storage node request or query node request is routed may be determined by the subscriber identifier, bucket identifier and eID specified in the request.

0210Once information is added to an eID store, indexes for the eID store may be built. As described above, each eID in the eID store has an associated set of attributes stored as {name, value) pairs. Each name corresponds to an index, and each index corresponds to a particular name for a {name, value) pair. In one embodiment, the indexes (each row in the index) may be sorted by the values associated with the names. In one embodiment, the indexes may be stored in a local query index store associated with the local eID store. Note that the indexes are specific to the particular bucket. In one embodiment, however, indexes may be concatenated across buckets to avoid having many small data structures if there are many small buckets.

0211As an example, an eID store, and associated index, may be constructed for a database of information (the data store) on articles of merchandise for sale, for example books at an online commercial website that offers the books for sale. One attribute of the articles may be the sale price of the article. Thus, eIDs for the information on the articles in the database may be provided and added to the eID store. Each eID may have an associated set of {name, value} pairs that represent names and values for various attributes of the associated article. For example, one of these {name, value} pairs for the articles may be “Sale Price -<dollar amount>”. Thus, an index may be created for the attribute name “Sale Price”. This index may be sorted by the value of “Sale Price”. A client may submit a query request that includes a query expression that indicates that the client is requesting eIDs for all articles with a certain “Sale Price” value, with a “Sale Price” value less than a specified amount, and so on. The indexes may then be used to find which article(s) in the data store have a “Sale Price” value that satisfies the query expression. All eIDs for articles in the data store that have a “Sale Price” value that satisfies the query may be returned in the query results to the querying client.

0212In one embodiment, the storage subsystem <b>206</b> may initialize a bucket as one partition. As information is added to the bucket, the bucket may eventually grow until the bucket is at or near the point of being too large to fit on one storage node. At some point before the available storage space on the storage node becomes critically low (in other words, while available storage space on the storage node is still in a comfort zone), the bucket may be repartitioned into two (or more) partitions, and one (or more) of the partitions may then be moved onto another storage node so that the bucket can continue to grow This repartitioning of the bucket may be performed transparently to the client application. Note that partitioning may also be performed for other reasons, for example to provide load-balancing for service requests. A partitioning mechanism for the searchable data service is further described later in this document.

0213Embodiments of the searchable data service may provide an interface that allows clients to delete entries that were previously added to a bucket. In one embodiment, these entries may be marked as deleted in an eID store, but are not removed from disk. In another embodiment, these entries may be marked for deletion, and the searchable data service may provide a mechanism that periodically or aperiodically performs garbage collection to remove any entries that have been marked for deletion from disk. In one embodiment, if a bucket has been previously repartitioned to create two or more partitions, and subsequently entries have been deleted from the bucket, the searchable data service may provide a mechanism that may merge two or more partitions into one partition, if there is sufficient disk space on a storage node to store the single, merged partition.

0214Repartitioning of a bucket may be performed when the bucket (or a partition of the bucket) is at or near the point of being too large to fit on a single storage node. Thus, repartitioning of buckets as described herein may allow a bucket to grow as the storage requirements of the client grow. Replication of partitions across two or more storage nodes, on the other hand, may be performed, for example, to provide redundancy, data durability, data availability and load sharing among the storage nodes and/or across data centers. Replication of a partition to two or more storage nodes within a data center or across data centers may be performed even for a bucket that has only one partition.

0215Note that, in one embodiment, a searchable data service may be implemented on nodes, or hosts, that physically reside in two or more data centers. Each data center may include two or more nodes that participate in the searchable data service implementation. Searchable data service nodes in a data center may include, but are not limited to, one or more coordinator nodes (nodes that host an instance of the request router <b>202</b>), one or more query nodes, and one or more storage nodes. A partition on a storage node within a data center may be replicated to one or more other storage nodes within that data center, and/or may be replicated to one or more other storage nodes in one or more other data centers. Replication within a data center may protect against node failures within the data center and may provide load-balancing among nodes within the data center. Replication across data centers may protect against data center-level failures, and may provide load-balancing across data centers.

0216In one embodiment where the searchable data service is implemented across two or more data centers, a bucket with a single partition may have at least four replicas of the partition. In any particular data center where this bucket resides, the partition may be replicated to at least two storage nodes, and may also be replicated to at least one other data center. In the other data center(s), the partition may be replicated to at least two storage nodes within the data center(s). If the bucket has more than one partition, each partition may be similarly replicated across storage nodes within a data center and/or may be replicated to storage nodes across data centers.

0217In one embodiment, a lazy replication mechanism may be used in the replication of partitions. In one embodiment, when replicating a partition, there may be two types of communication among nodes that are performed. In one embodiment, replication of partitions may be performed at least in part using a gossip protocol-based communication mechanism among searchable data service nodes and components within and across data centers, in combination with an anti-entropy-based communication mechanism. The anti-entropy protocol may provide faster communication than a gossip protocol. Using the anti-entropy protocol, the entire data structure of the partition may be replicated to another storage node to ensure initial consistency. In the meantime, however, updates may be received and applied to the original partition. Therefore, updates to the original partition that are received on the original storage node while the anti-entropy replication is occurring may be propagated to the new replica on the other storage node using the gossip protocol. The replica of the partition that is replicated via anti-entropy gets progressively older as time passes. However, any updates that are received are gossiped to the new replica. When the anti-entropy replication of the partition is completed and the new replica is ready to come on-line, the new replica may be up-to-date because of the gossiped updates.

0218In one embodiment, the searchable data service may attempt to provide as close to 24/7 availability and reliability of searchable indexes to clients as possible, and may provide a mechanism through which searchable indexes are ensured to be available and up-to-date with any additions or modifications if a storage node or even an entire data center becomes unavailable for some reason. Replication of partitions across storage nodes both within data centers and across data centers is part of this mechanism. To help ensure that available replicas are up-to-date, in one embodiment, when an entry for an entity in a data store is added to or modified in a local eID store on a storage node, the change made to the local eID store on the storage node may be made to one or more other eID stores on other storage nodes by an update service of the storage subsystem <b>206</b>. In one embodiment, an instance of an eID update manager component on each storage node may implement the functionality of the update service on the storage node. In one embodiment, the update service ensures that each update is-applied to two or more replicas on other storage nodes, but not necessarily to all replicas. The gossip protocol among the storage nodes may then be used to propagate the update to all replicas.

0219In one embodiment, when an update to a local eID store on a storage node in a data center is made, and before a response is returned to the client indicating that the update was successful, the update service of the storage subsystem <b>206</b> may act to ensure that the update has been made to at least one other local eID store on a storage node in the data center and to at least one other local eID store on a storage node in another data center. In one embodiment, when there is an initial update made in a local eID store on a storage node within a data center, the update service of the storage subsystem <b>206</b> waits for confirmation that the update has been successfully made to at least two local storage nodes and to at least one storage node in another data center before a response is sent to the client that the update was successful. Thus, if the original storage node or even the entire data center goes offline for some reason, an up-to-date replica may be available on another storage node in the same data center and/or on another storage node located in a different data center. Note that the update may be propagated to other storage nodes not updated by the update service using the gossip protocol so that all replicas of the partition are weakly maintained as consistent, even though the client may be informed that the update has been successfully made before the update has been propagated to all storage nodes that host replicas of the partition.

0220The storage nodes that replicate a particular partition or partitions of a bucket may be considered a replication group. The storage nodes in a replication group may have identical, or nearly identical, copies or replicas of the partitions. In one embodiment, updates to the partition(s) may be propagated to the storage nodes within the replication group using the gossip protocol. Therefore, “identical” may be subject to the limitations of the gossip protocol, which provides weak consistency. At any given point in time, the partitions within a replication group are not necessarily identical, but converge to be identical as the updates are propagated via the gossip protocol.

0221In one embodiment, the number of replicas of a partition that are maintained in a replication group may be dependent on monitored availability and reliability statistics of the hardware within the data center. If the searchable data service detects that the hardware is not particularly reliable or available, more replicas may be created within a replication group. More reliable and available hardware may allow fewer replicas to be maintained. In one embodiment, there may be at least four and up to six replicas of a partition in a replication group. Note that this pertains to replicas created and maintained to provide durability, reliability, and availability of the data. In one embodiment, the number of replicas of a partition that are maintained in a replication group may be dependent on monitored availability and reliability statistics of the hardware across two or more data centers, for example if the replication group extends across two or more data centers. In one embodiment, the number of replicas of a partition that are maintained in a replication group may also be at least in part a function of the operational characteristics of a network. In this embodiment, for example, data redundancy may be increased based on factors that may include one or more of, but are not limited to, failure modes on a network, response times on the network, error rates for data retrieval on the network, or on one or more other factors or combinations thereof.

0222In one embodiment, replication of partitions may also be performed in situations where a particular partition or a particular replica of a partition is detected to be very read active, with large numbers of reads (query messages) being received for the partition or for a particular replica within the replication group, by a group membership and health component of the searchable data service. The searchable data service, upon detecting that the partition or replica is receiving queries to the extent that it is approaching being out of a comfort zone for reads, may create one or more additional replicas of the partition to distribute the queries across more replicas and thus to provide load-balancing of the read (query) load across additional storage nodes.

0223If a high write load to a bucket (e.g., messages from the client to add or update entries in the bucket) is detected, creating additional replicas of a partition or partitions within the bucket may not help. Instead, creating additional replicas may be counterproductive, since updates are propagated to replicas using the gossip protocol, and more replicas tends to generate more gossip within a replication group. Therefore, in one embodiment, if a bucket is detected to be write active by the searchable data service to the point that at least some storage nodes may be nearing the boundary of their comfort zone, the searchable data service may repartition the bucket, rather than creating more replicas of partitions, so that the data in the bucket is spread across more storage nodes, and thus the write load may be load-balanced across more storage nodes.

0224In one embodiment, a storage node that has a partition that needs to be replicated may communicate this information to one or more other storage nodes, for example using the gossip protocol. One or more of the other storage nodes, within the data center or in another data center, may then volunteer to receive a replica of the partition. Information on the actual replication to another storage node may be communicated to other components on nodes of the searchable data service (for example, to storage node locators on coordinator nodes and query nodes) so that the status of replicas within a domain (within a bucket) of the searchable data service may be tracked.

0225Information on the repartitioning of a partition on a storage node may be similarly communicated to other components on other nodes so that the status of partitions within a domain of the searchable data service may be tracked. If a partition needs to be moved from one storage node to another storage node, this information may be communicated to one or more other storage nodes, and storage nodes that receive this information may then volunteer to receive the partition. The storage node that needs to move a partition may then select a best candidate storage node to receive the partition. An exemplary stress management mechanism that implements a stress management algorithm for managing disk load on storage nodes in one embodiment of a searchable data service system, and that may be used to select a best candidate storage node from among two or more candidate storage nodes to receive a partition, is described later in this document in the section titled <i>Stress Management</i>.

0226Instead of repartitioning or replicating a partition as a reactionary response to problems or crises, the searchable data service may provide one or more mechanisms that enable nodes to monitor the use and health of various resources on the nodes, including storage resources on storage nodes within the storage subsystem <b>206</b>, to share the health information among nodes within the searchable data service, and to proactively work to avoid potential high stress or load on various resources within the searchable data service. In one embodiment, comfort zones may be defined for various resources in the searchable data service, and the searchable data service may proactively work to keep the resources within their respective comfort zones.

0227The searchable data service may perform a particular action or actions when it is detected that a resource is getting near the edge of its comfort zone. For storage nodes in storage subsystem <b>206</b>, these actions may include, but are not limited to, replicating and repartitioning. The searchable data service may monitor the use and health of the storage nodes, as well as other types of resources such as query nodes and coordinator nodes, and may attempt to perform an action (e.g., repartitioning or replication for storage nodes) in advance of a potential crisis (i.e., when the resource is still within the comfort zone) as opposed to waiting until the resource is already under stress. If the system were to wait until a resource is already under stress to perform some action in an attempt to relieve the stress, such as repartitioning or replication, the resource may already be being overloaded with internal and external requests, making it more difficult to perform the action. Thus, the searchable data service provides a proactive approach to health management to support the availability and reliability of resources within the system as opposed to a reactive approach.

0228In one embodiment, each node in the searchable data service may include an instance of a node manager component that may serve as a control and monitoring agent for the node. The node manager component may serve as a self-monitoring agent that may monitor health information for various resources on the node, which may include, but is not limited to, disk space usage, bandwidth usage, CPU usage, read and/or write load, etc.

0229In one embodiment, a stress manager component on each node in the searchable data service may detect if a health metric for a resource on the node, collected by the node manager, is at or near the limits of its comfort zone, and may, in response to said detection, initiate an appropriate action. The stress manager may implement one or more algorithms that may be used to determine an action or actions to be taken when a resource is at or near the limit of its comfort zone. For example, when the available storage space on a storage node is nearing the edge of its comfort zone, the stress manager may initiate repartitioning on the node so that a newly-created partition may be moved to another storage node, thus freeing disk space on the storage node. Note that repartitioning would actually be performed under the control of a local partition manager.

0230The node manager component may enable the nodes to participate in monitoring and maintaining the global health of the searchable data service implementation. The node manager component monitors the health of resources on a particular node. In one embodiment, another component may monitor the health of other nodes in a local neighborhood or node group to compare the health of the node to other nodes.

0231In one embodiment, each node in the searchable data service may have an instance of a group membership and health component. In one embodiment, the group membership and health components on the various nodes may allow health information collected locally on nodes to be communicated to other nodes within a local neighborhood or node group of the searchable data service. In one embodiment, the group membership and health component allows other components of the searchable data service to identify sets of nodes to be monitored, and to then query for automatically refreshed health information about those nodes. The group membership and health component may serve, for example, as a failure detection mechanism. The group membership and health component may also allow a node to compare its local health with other nodes in its neighborhood or group.

0232In one embodiment, each node in the searchable data service may make local decisions based on the health of its local resources and the health messages that it receives from other nodes within its neighborhood or node group through the group membership and health mechanism. This may distribute health monitoring and management of resources of the searchable data service among the local nodes and node groups, rather than relying on a central controller. Thus, in one embodiment, there may be no central controller that monitors the health of the entire searchable data service implementation and attempts to optimize resources, and thus no single point of failure. Since health monitoring and maintenance is performed locally on nodes and cooperatively within node groups instead of by a central controller, a global list of health information does not have to be maintained, and less health information has to be communicated globally across the entire searchable data service implementation.

0233Through a local node manager, each node tracks its own resource usage and health. Each node may also monitor the health of other nodes within a local neighborhood or group. A local stress manager accesses the resource usage and health information collected by the node manager. If the stress manager on a storage node determines that the node needs to repartition its data, the storage node does not force another storage node to accept the newly-created partition. Instead, this information may be shared with other local storage nodes, for example through the group membership and health mechanism. Other local storage nodes that have available disk space (again, locally monitored by the node manager) may look for other storage nodes that need to repartition in the health information shared through the group membership and health mechanism. If a storage node that has available disk space finds another storage node that needs to move a partition, the storage node may voluntarily decide to accept the partition.

0234Thus, storage nodes in a particular group may agree among themselves on the repartitioning of data. This may not be necessarily performed as a group decision in which all nodes participate. Instead, two storage nodes may agree to cooperate to repartition data, with one of the nodes voluntarily accepting the new partition. Note that this group communication and cooperation may occur among nodes within a particular data center, but may also occur among nodes across data centers.

0235Initially, when a bucket is created, the bucket includes one partition. The partion may be replicated across two or more storage nodes, which form a replication group. When the replicated partition is repartitioned to form two or more new partitions, each new partition becomes a replication group. Initially, the newly created partitions remain on the same storage nodes. Thus, each storage node may be a member in one or more replication groups. Repartitioning of the partition is performed on all of the storage nodes in the replication group; there is still one bucket; and initially all of the data remains in the same place. Half of the data, however, is in partition A, and the other half is in partition B. Potential storage space problems on any of the storage nodes have not been solved by repartitioning, however, because the replicas are still on the same storage nodes. Each storage node, if nearing the limits of its available storage space comfort zone, may decide to move a partition to another storage node, if possible. In one embodiment, another storage node, which in one embodiment may be located via a gossip protocol, may voluntarily decide to receive the partition. Copying the partition to the other storage node may be performed using an anti-entropy mechanism to replicate the partition, with a gossip protocol used to apply any updates to the replica of the partition. This moving of partitions may be performed proactively, while available storage space is still within the comfort zone, to help avoid crisis situations.

0236As mentioned above, one type of node group is a replication group. Each storage node in a replication group stores a replica of a particular partition. As the partition grows, any one of the storage nodes in the replication group may detect that available storage space on the node is nearing the limits of its comfort zone, and thus the local replica may need to be partitioned. In one embodiment, if a partition is getting too large for any one of the storage nodes within a replication group, the partition may be repartitioned on all of the storage nodes within the replication group, even if there is disk space available on the other storage nodes. The newly created partitions may each constitute a separate replication group, though initially all the partitions may remain on the same set of storage nodes. Thus, repartitioning a replicated partition also generates two replication groups where formerly there was one replication group. One of the storage nodes that is at or near the limits of its comfort zone for available storage space may then move its replica of one of the newly created partitions to another storage node that volunteers to receive the partition. For example, another node may join or be added to the replication group, and may voluntarily receive the partition. Other storage nodes in the replication group(s) may have enough disk space, and so may not move a partition.

0237<figref idref="DRAWINGS">FIG. 4</figref> illustrates an exemplary network architecture for a searchable data service according to one embodiment. A searchable data service implementation may include, but is not limited to, a Web services platform <b>200</b>, one or more coordinator nodes <b>350</b>, one or more query nodes, referred to as query TSAR (Top Search AggregatoR) nodes <b>360</b>, and one or more storage nodes <b>370</b>. Each coordinator node <b>350</b> may include, but is not limited to, at least one instance of request router <b>202</b>.

0238Note that the high-level, functional query subsystem <b>204</b> and storage subsystem <b>206</b> described in <figref idref="DRAWINGS">FIG. 3</figref> may, but do not -necessarily map directly onto query TSAR nodes <b>360</b> and storage nodes <b>370</b>, respectively. Each of the Subsystems may include several components, which are further described below in reference to <figref idref="DRAWINGS">FIG. 6</figref>. In one embodiment, components of the query subsystem <b>204</b> reside on the query TSAR nodes <b>360</b>, and components of the storage subsystem <b>206</b> map onto the storage nodes <b>370</b>. Alternatively, particular components that may be viewed as functionally part of one of the Subsystems may physically reside on a coordinator node <b>350</b>, a query TSAR node <b>360</b>, or a storage node <b>370</b>. For example, each storage node <b>370</b> may include an instance of a local query processor <b>228</b> of <figref idref="DRAWINGS">FIG. 6</figref>, which may be, but is not necessarily, functionally viewed as a component of the query subsystem <b>204</b>. In addition, some components of the searchable data service illustrated in <figref idref="DRAWINGS">FIG. 6</figref> may have local instances on different ones of the nodes. For example, in one embodiment, there may be a local instance of storage node locator <b>216</b> on each coordinator node <b>350</b> and on each query TSAR node <b>360</b>.

0239Data store <b>332</b> represents a data storage system in which units of data (entities) may be stored. Data store <b>332</b> may be implemented in accordance with any type of storage system in which locators may be used to locate and retrieve entities. An application may be implemented on client system <b>330</b> that leverages the searchable data service as a search frontend to the backend data store <b>332</b>. In one embodiment, the application may be configured to access the functionalities of the searchable data service in accordance with a Web service interface of the Web services platform <b>200</b> to search for and retrieve data in the backend data store <b>332</b>.

0240An application that leverages the searchable data service as a search frontend to a backend data store <b>332</b> may be referred to as a subscriber to the searchable data service. Note that a searchable data service implementation may have two or more subscribers. In other words, a searchable data service implementation may provide searchable indexes to two or more backend data stores. Also note that an application may leverage a searchable data service implementation as a search frontend to two or more backend data stores <b>332</b>. An application that leverages the searchable data service as a search frontend to two or more backend data stores <b>332</b>, and for which there are thus two or more searchable indexes implemented in the searchable data service implementation, may be identified separately and uniquely as a subscriber for each searchable index. A unique subscriber identifier may be assigned for each subscription to the searchable data service, and the subscriber identifiers may be used to uniquely identify particular searchable indexes to particular data stores <b>332</b>. Note that two or more client systems <b>330</b> may access a particular searchable index in a searchable data service implementation using an associated unique subscriber identifier.

0241In one embodiment, a client system <b>330</b> may submit service requests (query node requests and/or storage node requests) to the searchable data service in accordance with the Web service interface of the Web services platform <b>200</b> via Internet <b>334</b>. The Web services platform <b>200</b> may route the service request(s) to a coordinator node <b>350</b>. A coordinator node <b>350</b> routes the service requests to the appropriate node(s), collects results, and sends the results back to the Web services platform <b>200</b>. A request router on the coordinator node <b>350</b> may receive the service request(s) from the Web services platform <b>200</b> and determine whether each service request is a storage node request or a query node request. If a service request is a storage node request, the request router queries a storage node locator to map the eID and bucket specified in the request to the appropriate storage node(s) <b>370</b>. If the service request is a query node request, the request router queries a query node locator to map the bucket and query expression to an appropriate query TSAR node <b>360</b>. In one embodiment, the storage node locator and the query node locator may be components of the searchable data service with instances located on each coordinator node <b>350</b>.

0242Upon receiving a query node request from a coordinator node <b>350</b>, a query TSAR node <b>360</b> may perform processing of the query before forwarding the query to one or more storage nodes <b>370</b>. The query TSAR node <b>360</b> may forward the query to appropriate storage node(s) <b>370</b> for execution of the query. For a small domain, a query typically may run on a single storage node <b>370</b>. Larger domains may be partitioned across multiple storage nodes <b>370</b>, requiring queries to be executed on one storage node <b>370</b> for each partition. Partitioning is further described later in this document. The query TSAR node <b>360</b> may use a local instance of a storage node locator to locate appropriate storage node(s) <b>370</b> for the query. The query TSAR node <b>360</b> may aggregate and sort query results received from storage node(s) <b>370</b>. The query TSAR node <b>360</b> may then return the query results to the coordinator node <b>350</b>. In one embodiment, the query TSAR node <b>360</b> may paginate the query results, if necessary or desired.

0243On a storage node <b>370</b>, an eID store may serve as the authoritative store for eIDs and their attributes. Indexes may be built from the eID store that may index all attributes for eIDs on the local storage node <b>370</b>. A local query processor may run queries received from query TSAR node(s) <b>360</b> against the indexes on the storage node <b>370</b>. An eID update service may receive storage node requests from a coordinator node <b>350</b> and update the eID store accordingly. A local partition manager may observe the use of local resources (e.g., disk space, CPU load, network bandwidth, etc.) for the storage node <b>370</b>, and may communicate with other partition managers on other storage nodes <b>370</b> to redistribute partitions when necessary.

0244<figref idref="DRAWINGS">FIGS. 5A and 5B</figref> illustrate a method for implementing a searchable data service that processes service requests to store searchable data service objects in a searchable index and to locate entity identifiers (eIDs) for entities in a data store in the searchable index according to one embodiment. Each searchable data service object may specify two or more attributes of a particular entity in the data store. Each attribute may be expressed as a {name, value} pair, and the attributes may include a unique entity identifier (eID) for locating a particular entity in the data store.

0245A searchable data service system may be implemented on a plurality of nodes. The nodes may be located in one data center or may be dispersed across two or more data centers. The data centers may be geographically dispersed. In one embodiment, the searchable data service may include at least a coordination subsystem, a query subsystem and a storage subsystem. In one embodiment, the plurality of nodes may include one or more coordinator nodes that implement the coordination subsystem, one or more query nodes (also referred to as query TSAR nodes) that implement the query subsystem, and one or more storage nodes that implement the storage subsystem. In one embodiment, a Web services platform may provide a Web service interface to the searchable data service that provides one or more interface calls to client applications of the searchable data service.

0246In <figref idref="DRAWINGS">FIG. 5A</figref>, the Web services platform may receive service requests from a client application in accordance with the Web service interface to the searchable data service, as indicated at <b>1000</b>. The Web services platform may then forward the service requests to a coordinator node of the searchable data service, as indicated at <b>1002</b>. In one embodiment, the Web services platform may provide one or more other services that perform metering, billing, authentication, and access control of subscribers to the searchable data service.

0247As indicated at <b>1004</b>, the coordinator node may determine if the service request is a query node request (a read operation to the searchable index) or a storage node request (a write operation to the searchable index, or a list attributes request). In one embodiment, a request router component of the searchable data service may perform said determining. At <b>1004</b>, if the service request is a storage node request, the coordinator node may locate a storage node to receive the storage: node request, as indicated at <b>1006</b>. In one embodiment, a request router component of the searchable data service may consult a local storage node locator component of the searchable data service to locate a storage node to receive the storage node request. As indicated at <b>1008</b>, the coordinator node may then forward the storage node request to the determined storage node.

0248Upon receiving the storage node request, the storage node may modify a partition of a searchable index in accordance with the storage node request, as indicated at <b>1010</b>. In one embodiment, the storage node may: <ul id="ul0026" list-style="none"><li id="ul0026-0001" num="0249"> add a searchable data service object specified in the storage request to the searchable index; modify a searchable data service object stored in the searchable index as specified in the storage request; </li><li id="ul0026-0002" num="0250"> delete a searchable data service object from the searchable index as specified in the storage request; or </li><li id="ul0026-0003" num="0251"> compile and return a list of all {name, value} pairs for an entity if the storage node request is a list attributes request. Note that a list attributes request may not result in modification of the partition. </li></ul>

0252As indicated at <b>1012</b>, changes to the partition may be propagated to one or more other storage nodes that store a replica of the modified partition. In one embodiment, the changes may be propagated to other storage nodes in accordance with a gossip protocol. In one embodiment, an anti-entropy protocol may also be used to propagate changes to other replicas of the partition. As indicated at <b>1014</b>, a response indicating success or failure of the storage node request may be returned to the client application in accordance with the Web service interface.

0253At <b>1004</b>, if the service request is a query node request, the coordinator node may locate a query node to receive the query node request, as indicated at <b>1016</b>. In one embodiment, a request router component of the searchable data service may consult a local query node locator component of the searchable data service to locate a query node to receive the query node request. As indicated at <b>1018</b>, the coordinator node may then forward the query node request to the determined query node. Item <b>1020</b> indicates that the flowchart is continued in <figref idref="DRAWINGS">FIG. 5B</figref>.

0254In <figref idref="DRAWINGS">FIG. 5B</figref>, the query node receives the query node request from the coordinator node and processes the query node request. In one embodiment, the query node may perform some preprocessing of the query node request, for example normalization of an unnormalized query expression specified in the query node request. As indicated at <b>1022</b>, the query node may determine if the query expression specified in the query node request can be satisfied from a local query cache that caches results from previous query node requests. At <b>1024</b>, if the query node can be satisfied from the local query cache, then, as indicated at <b>1026</b>, the query node may return query results retrieved from the local query cache to the client application in accordance with the Web service interface.

0255At <b>1024</b>, if the query node request cannot be satisfied from the local query cache, then, as indicated at <b>1028</b>, the query node may locate one or more appropriate storage nodes to receive and process the query node request. In one embodiment, the query node may consult a local storage node locator component of the searchable data service to locate the one or more storage nodes to receive the storage node request. As indicated at <b>1030</b>, the query node may then forward the query node request to the determined storage node(s).

0256As indicated at <b>1032</b>, each storage node that receives the query node request from the query node may search a local partition of the searchable index to locate searchable data service objects that satisfy the query expression specified by the query node request. As indicated at <b>1034</b>, each of the storage nodes may then return query results that satisfy the query expression to the query node. In one embodiment, the query results may be cached in a local query cache, as indicated at <b>1036</b>. The query node may merge, sort, and/or paginate the query results, as necessary or desired, as indicated at <b>1038</b>. If query results are received from more than one storage node, then the query results may need to be merged. If the query results exceed a page limit, then the query results may be paginated, and then may be returned to the client application in two or more response messages. In one embodiment, the query results may be sorted according to a sort criteria specified in the query node request. In one embodiment, the query results may include at least the entity identifiers (eIDs) from each searchable data service object in the searchable index that satisfied the query expression specified in the query node request. As indicated at <b>1040</b>, the query node may return the query results received from the storage node(s) to the client application in accordance with the Web service interface.

0257<figref idref="DRAWINGS">FIG. 6</figref> illustrates an exemplary lower-level, modular architecture for a searchable data service, according to one embodiment. This Figure shows the data flow through various modules, or components, of the searchable data service. In this embodiment, the searchable data service may include one or more of, but is not limited to, the components shown. Note that an implementation of the searchable data service may include two or more of at least some of the illustrated components.

0258The following describes exemplary data flow in an embodiment of the searchable data service when new information is submitted to the searchable data service using an add request (a type of storage node request) to a Web services API provided by the Web services platform <b>200</b>. The REST or SOAP request comes to the Web services platform <b>200</b> where it is authenticated, time-stamped and passed on to the request router <b>202</b>. The request router <b>202</b> asks the storage node locator <b>216</b> for a list of one or more storage nodes <b>270</b> that may store the data, and sends the data to one node on that list. The entity ID update manager <b>230</b> on the storage node <b>270</b> receives the data, stores the data on its local entity ID store <b>236</b>, and sends the data to at least one more local storage node <b>270</b> and at least two storage nodes <b>270</b> in another data center. When all these storage nodes have stored the data, the REST or SOAP call returns a “success” result.

0259The following describes exemplary data flow in an embodiment of the searchable data service when processing a query node request, or query. The REST or SOAP request comes to the Web services platform <b>200</b>, where it is authenticated and passed on to the request router <b>202</b>. The request router <b>202</b> asks the query node locator <b>220</b> for a list of query TSARs (Top Search AggregatoRs) <b>212</b> that can process the query, and routes the query to one node (query TSAR <b>212</b>) on that list. The query TSAR <b>212</b> first determines if the query can be satisfied from query cache <b>214</b>. If so, it returns the query response to the request router <b>202</b>, which forwards the query response back to the Web services platform <b>200</b>, from where the query response may be returned to a client application that initiated the query in accordance with the Web service interface.

0260If the query cannot be answered out of query cache <b>214</b>, the query TSAR <b>212</b> asks a local storage node locator <b>216</b> for a set of partitions of a bucket, and the storage node hosts that store replicas of those partitions. The query TSAR <b>212</b> may then send the query to the local query processor <b>228</b> of one storage node host from each partition. The local query processors <b>228</b> may find all the eIDs that satisfy the query. These lists are then returned to the query TSAR <b>212</b>, where the lists are aggregated. The aggregated list may be sorted and returned to the querying client.

0261Embodiments of a searchable data service may run on large distributed systems with high availability and reliability requirements. In these environments, embodiments of the searchable data service may monitor and manage the system resources to meet the high availability and reliability requirements. In one embodiment, a group membership and health component <b>226</b> may run on each node, and may communicate local health information about CPU, disk, memory, network utilization, and other local system metrics to one or more other nodes. Group health <b>226</b> component may track membership in replication groups, and may also track when nodes enter and leave the searchable data service system environment.

0262The partition manager <b>232</b> handles the assignment of storage node hosts to replication groups, and the splitting of buckets into multiple partitions. This enables nodes that are running low on disk space to partition datasets so that some of the data may be moved to another node. An exemplary algorithm for deciding when and how to split and move data is described later in this document.

0263In one embodiment, all searchable data service nodes may use the group communication component <b>222</b> to communicate with other searchable data service nodes. In one embodiment, the group communication component <b>222</b> may provide epidemic (gossip) and anti-entropy inter-node communication.

0264In one embodiment of the searchable data service, to order updates to the data store, for each update request, the request router <b>202</b> may generate a sequencing token and pass it back with the reply to the client. The sequencing token may capture an ordering ID and possibly other system information. The client may, if desired, extract the ordering ID from the sequencing token. In one embodiment, the searchable data service may apply requests in the order given by this ordering ID. Note that other embodiments may use other methods to order updates.

0265In one embodiment, ordering IDs may be generated by a request router <b>202</b> based on its local NTP synchronized time. Other embodiments may use other bases for generating ordering IDs. Note that NTP synchronized time is an imperfect synchronization system and that there may be times where update order may be inverted due to clock skew. However, in one embodiment using NTP synchronized time as a basis for generating ordering IDs, the client may determine the order in which the updates are applied and resubmit an update if they disagree with this order.

0266In one embodiment, the client may be requested to send the last sequencing token received by the client with its next request to the searchable data service. In one embodiment, the searchable data service may use the received last sequencing tokens to collect data regarding clock skew and ordering. In one embodiment, the searchable data service may use the last sequencing token supplied by the client to affect the ordering of updates, if necessary as determined by the collected data.

0000Data Partitioning and Replication

0267Embodiments of the searchable data service may provide one or more mechanisms for data partitioning and replication of indexing data in the storage subsystem <b>206</b> Data partitioning may allow clients of the searchable data service to store and maintain larger searchable indexes than can otherwise fit on a single storage node. Data replication may provide redundancy in the searchable index for the durability, reliability, and availability of the searchable index to a subscriber's data store stored and made accessible for queries from client applications via the searchable data service.

0268An aspect of data partitioning and data replication in embodiments of the searchable data service is that there is no central controller that controls data partitioning and data replication. Instead, data partitioning and data replication tasks may be distributed among various nodes and components in the searchable data service system.

0269<figref idref="DRAWINGS">FIG. 7</figref> illustrates a method for partitioning a searchable index in a searchable data service system according to one embodiment. A searchable data service system may be implemented on a plurality of nodes. The nodes may be located in one data center or may be dispersed across two or more data centers. The data centers may be geographically dispersed. In one embodiment, the searchable data service may include at least a coordination subsystem, a query subsystem and a storage subsystem. In one embodiment, the plurality of nodes may include one or more coordinator nodes that implement the coordination subsystem, one or more query nodes (also referred to as query TSAR nodes) that implement the query subsystem, and one or more storage nodes that implement the storage subsystem. In one embodiment, a Web services platform may provide a Web service interface to the searchable data service that provides one or more interface calls to client applications of the searchable data service.

0270As indicated at <b>1050</b>, the searchable data service may initialize a searchable index for a data store as a single partition stored on a single storage node. As indicated at <b>1052</b>, over time, the partition may grow. For example, the partition may grow as storage requests are received from a client application to add searchable data service objects to the searchable index. At some point, the searchable data service may detect that the available disk space on the storage node is at or near the limits of a comfort zone for available disk space on the storage node.

0271To allow the searchable index to continue to grow, the partition may be repartitioned to generate two or more new partitions, as indicated at <b>1054</b>. Each of the new partitions may include a different subset of the searchable data service objects in the searchable index. One or more of the new partitions may then be moved to one or more other storage nodes, thus freeing up storage space on the storage node, as indicated at <b>1056</b>. In one embodiment, another node may cooperatively volunteer to receive and store a new partition. In one embodiment, the storage node that needs to move a partition may broadcast a message within a group of storage nodes indicating that the storage node needs to move the partition. One or more of the storage nodes that receive the message may then volunteer to store the partition. The storage node may then select a best storage node from the volunteers to store the partition, and may then cooperate with the selected storage node to move the partition to the other storage node. Note that the different partitions stored on the two nodes may continue to grow, and thus may be repartitioned to generate new partitions that may then be moved to other storage nodes if necessary. Repartitioning and moving partitions to other storage nodes thus allows partitions of a searchable index to grow beyond the storage limits of a single storage node. An exemplary stress management mechanism that implements a stress management algorithm for managing disk load on storage nodes in one embodiment of a searchable data service system, and that may be used to select a best storage node from among two or more volunteer storage nodes to receive a partition, is described later in this document in the section titled <i>Stress Management</i>.

0272Note that repartitioning a partition to create two or more new partitions and moving one or more partitions from a storage node to one or more other storage nodes may also be performed to load-balance write load to the searchable index. If a storage node detects that write load to the partition is at or near the limit of a comfort zone for writes to the storage node, the storage node may repartition the partition and cooperatively move at least one of the new partitions to another storage node, as described above, to move some of the write load to the other storage node.

0273<figref idref="DRAWINGS">FIG. 8</figref> illustrates a method for replicating a partition of a searchable index in a searchable data service system according to one embodiment. Data replication may provide redundancy in the searchable index for the durability, reliability, and availability of the searchable index. Replication of a partition may also be performed to load-balance one or more usage metrics for a resource of the storage node. In one embodiment, replication of a partition may be performed to load-balance read load to the partition if the storage node detects that read load to the partition is at or near the limit of a comfort zone for reads to the storage node. In one embodiment, replication of a partition may be performed to load-balance CPU load on the storage node if the storage node detects that CPU load on the storage node is at or near the limit of a comfort zone for CPU load to the storage node.

0274To replicate a partition stored by the storage node, a storage node may locate another storage node to receive a replica of the partition, as indicated at <b>1100</b>. In one embodiment, the other node cooperatively volunteers to receive and store the replica. In one embodiment, the storage node that wants to replicate a partition may broadcast a message within a group of storage nodes indicating that the storage node is seeking a volunteer to receive the replica. One or more of the storage nodes that receives the message may then volunteer to store the replica. The storage node may then select a best storage node from the volunteers to store the replica, and cooperate with the selected storage node to replicate the partition to the other storage node.

0275As indicated at <b>1102</b>, the storage nodes may then cooperatively replicate the partition to the other storage node using an anti-entropy protocol. Note that the partition may potentially be updated during the replication as storage node requests for the searchable index are received and processed. To obtain consistency between the partition and the replica, in one embodiment, the replica may be updated with received updates to the partition using a gossip protocol to propagate the updates to the other storage node, as indicated at <b>1104</b>. Note that the gossip protocol may provide weak consistency between replicas of the partition. Also note that updates to replicas of a partition may continue to be performed using the gossip protocol to thus maintain weak consistency between the replicas.

0276The storage node to which the partition is replicated may be within the same data center as the storage node that stores the partition or may be in another storage center. In one embodiment, the searchable data service may create and maintain at least two replicas of a partition within a data center and at least two replicas of the partition within at least one other data center.

0000Data Partitioning

0277<figref idref="DRAWINGS">FIGS. 9A and 9B</figref> illustrate searchable indexes for subscribers, the segregation of data (eIDs) for each subscriber <b>250</b> into buckets, and partitioning of the buckets, according to one embodiment of the searchable data service. Searchable data service data, for each subscriber <b>250</b>, is segregated into buckets, which define the limits of data that may be considered in a single query. In <figref idref="DRAWINGS">FIG. 9A</figref>, when a searchable data service client (or subscriber) adds data to the searchable index that is identified by subscriber <b>250</b>A, the client submits a locator (eID), with attributes, into buckets <b>252</b>. Each bucket <b>252</b> initially resides on a single storage node. Since datasets may grow indefinitely, partitions may exceed the physical capacity of a disk on a storage node. To allow for this possibility, in one embodiment, the data in a bucket may be split across two or more partitions <b>254</b>, as illustrated in <figref idref="DRAWINGS">FIG. 9B</figref>. In <figref idref="DRAWINGS">FIG. 9B</figref>, the buckets <b>252</b> of <figref idref="DRAWINGS">FIG. 9A</figref> are shown have been split to form partitions <b>254</b>. For example, bucket <b>252</b>A has been split into partitions <b>254</b>A, <b>254</b>B and <b>254</b>C. Note that, in one embodiment, each partition <b>254</b> resides on a single storage node. However, more than one partition <b>254</b> may reside on a single storage node.

0278As partitions <b>254</b> grow, a disk may run out of space, requiring that one or more partitions <b>254</b> be moved to another storage node. In one embodiment, a stress manager component of the searchable data service may perform at least part of the task of managing the movement of partitions <b>254</b> among storage nodes. Data partitioning in embodiments of the searchable data service is further described below in reference to the partition manager <b>232</b> component and the stress manager component.

0000Data Replication

0279<figref idref="DRAWINGS">FIG. 9C</figref> illustrates data replication via replicating partitions according to one embodiment.

0280In one embodiment, for data durability and fault tolerance, data sets (bucket partitions <b>254</b>) may be replicated across several storage nodes. In <figref idref="DRAWINGS">FIG. 9C</figref>, the partitions <b>254</b> of <figref idref="DRAWINGS">FIG. 9B</figref> have been replicated to form replication groups <b>256</b>. For example, in <figref idref="DRAWINGS">FIG. 9C</figref>, partitions <b>254</b>A, <b>254</b>B, and <b>254</b>C of bucket <b>252</b>A have been replicated to form replication groups <b>256</b>A, <b>256</b>B, and <b>256</b>C. Replication may allow embodiments of the searchable data service to distribute query load across replication groups <b>256</b>, and thus may be necessary or desired as a response to sustained “read stress” on the searchable data service. In addition, as one or more storage nodes may fail, embodiments of the searchable data service may provision new storage nodes to keep the replication group(s) <b>256</b> populated. The details of forming replication groups is further described below in reference to the group membership and health component.

0000Partition Manager

0281In one embodiment, a partition manager <b>232</b> component of the searchable data service is responsible for making decisions and performing actions to reconfigure the searchable data service system to alleviate hot spots which may occur as a result of a shortage of disk (storage) space and/or from a high processing load. The partition manager <b>232</b> component may perform as a distributed computation (distributed across hosts or nodes) that tends towards balancing the stress on hosts or nodes in the searchable data service system.

0282In one embodiment, the partition manager <b>232</b> may perform one or more of, but not limited to, the following actions: <ul id="ul0027" list-style="none"><li id="ul0027-0001" num="0283"> A host (storage node) may be added to a replication group <b>256</b>. </li><li id="ul0027-0002" num="0284"> A host (storage node) may be removed from a replication group <b>256</b>. </li><li id="ul0027-0003" num="0285"> A partition <b>254</b> may be split. </li><li id="ul0027-0004" num="0286"> A partition <b>254</b> may be merged with another partition. </li></ul>

0287In one embodiment, the partition manager <b>232</b> performs these actions in accordance with group health information collected by and received from the group membership and health component <b>226</b>.

0000Partitions

0288In one embodiment, partitions <b>254</b> may be formed based on a hash of the entity ID (eID). The following is an exemplary function that returns a Boolean (true or false) indicating whether a provide eID is within a particular partition: <tables id="TABLE-US-00003" num="3"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="35PT" align="left" /><colspec colname="1" colwidth="182PT" align="left" /><thead><row><entry /><entry /></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry /><entry>bool inPartition(String eID, int mask, int value)</entry></row><row><entry /><entry>{</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="49PT" align="left" /><colspec colname="1" colwidth="168PT" align="left" /><tbody valign="top"><row><entry /><entry>int h = hash(eID);</entry></row><row><entry /><entry>return (h &amp; mask) == value;</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="35PT" align="left" /><colspec colname="1" colwidth="182PT" align="left" /><tbody valign="top"><row><entry /><entry>}</entry></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0289Any of a variety of hash functions may be used in various embodiments. In one embodiment, the hash function may be specified explicitly to support cross-platform implementations of the searchable data service. In one exemplary embodiment, CRC32, as defined in ISO 3309, may be used as the hash function for determining partitions. CRC32 may generate a smooth distribution for just about anything except intentionally malicious input. In one embodiment, the possibility of malicious input may be avoided by using a cryptographically-secure hash, with a tradeoff of greater computational expense.

0000Splitting and Merging Partitions

0290Searchable data service data is segregated into buckets <b>252</b>, which define the limits of data that may be considered in a single query. In one embodiment, buckets <b>252</b> which are queried may be replicated beyond the minimum number required for fault-tolerance so that arbitrary amounts of query-processing power may be added to a bucket <b>252</b>. However, a bucket <b>252</b> may become too large to be stored on hosts within the searchable data service system and/or may receive an excessive number of updates from client systems. Replicating buckets <b>252</b> may not address problems which may result from these potential situations. In one embodiment, to address these potential situations, buckets <b>252</b> may be divided into separate partitions <b>254</b> of data.

0291In one embodiment, updates to the data store need only be sent to a member of the partition <b>254</b> containing the entity to be updated. Queries, however, are made to all partitions <b>254</b> in a bucket <b>252</b>; the results of a query are then merged by a query aggregator in the query subsystem <b>204</b>. Therefore, the number of partitions <b>254</b> may be determined by the storage requirements of the bucket <b>252</b>, while the number of hosts in each replication group <b>256</b> may be driven by the number of queries for the bucket <b>252</b>.

0292Embodiments of the searchable data service may provide a mechanism, similar to extensible hashing, that allows the incremental scaling of a bucket <b>252</b> by adding single, potentially heterogeneous, hosts to a replication group <b>256</b>. This mechanism may allow a searchable data service system to take advantage of heterogeneous machines, and may enable the partitioning for a bucket <b>252</b> to be dynamically changed, among other benefits. In one embodiment, an algorithm for partitioning searchable data service entities may be employed in which the entity identifier (eID) is hashed to an interger, and the least significant bits of that integer are examined to determine a partition <b>254</b>. In one embodiment, the number of significant bits that are examined may vary between partitions <b>254</b>.

0293<figref idref="DRAWINGS">FIG. 10</figref> illustrates the splitting of partitions in replication groups according to one embodiment. In this embodiment, the number of partitions <b>254</b> in a bucket <b>254</b> may be increased by splitting partitions <b>254</b> in a replication group <b>256</b>. The replication group <b>256</b> for the given hash suffix becomes two partitions (two replication groups) corresponding to the two suffixes that may be formed by adding one more bit to the suffix. In the example illustrated in <figref idref="DRAWINGS">FIG. 10</figref>, the replication group <b>256</b>N of the hash suffix_<b>10</b> has been split into two partitions (replication group <b>256</b>N_and replication group <b>256</b>N_<b>1</b>) that are identified by the suffixes_<b>010</b> and _<b>110</b>.

0294Using this mechanism, the initial membership of the two new replication groups <b>256</b>N_<b>0</b> and <b>256</b>N_<b>1</b> may be exactly the same as the membership of the split replication group <b>256</b>N. No data migration initially happens, and queries and updates may be distributed as before the split. However, when a new storage node is added to one of the split replication groups <b>256</b> (in this example, replication group <b>256</b>N_<b>0</b>), the replication group has more than the required number of members. A stressed host may then leave the replication group <b>256</b>N_<b>0</b> (while remaining in the replication group <b>256</b>N_<b>1</b>), in this case by deleting half of its data (the half in replication group <b>256</b>N_<b>0</b>), thus alleviating the stress on the host. Thus, adding a single node to a bucket <b>252</b> may alleviate at least some stress on the storage subsystem.

0295Note that, if all hosts have the same amount of disk space (i.e., are homogeneous in regards to disk space), and if the data are more-or-less evenly divided among the partitions <b>254</b>, then all hosts in the bucket <b>252</b> may tend to run out of space at about the same time, which may require the number of hosts in the bucket <b>252</b> to double each time the bucket needs to repartition.

0296To help avoid having to double the hosts in a bucket <b>252</b> each time the bucket needs to partition when using homogeneous hosts, embodiments of the searchable data service may use one or more mechanisms that may add hosts more or less randomly, with the probability of hosts being added to a stressed replication group <b>256</b> increasing in proportion to the measured stress on that replication group <b>256</b>. Using these mechanisms, splitting of a replication group <b>256</b> may be performed before the storage stress on the replication group becomes critical. One or more new hosts may be added to the split replication groups <b>256</b> early, when stress is lower, with new hosts added more frequently as the measured stress level grows.

0000Partition Manager Interfaces

0297In one embodiment, the partition manager <b>232</b> may interact with the eID update manager <b>230</b> in accordance with an API. The following is an exemplary API that may be used by the partition manager <b>232</b> and that may include one or more of, but is not limited to, the described exemplary calls and callbacks. <ul id="ul0028" list-style="none"><li id="ul0028-0001" num="0298"> setpartitions(Subscriber, Bucket, AcceptPartitionList, DropPartitionList) </li></ul>

0299AcceptPartitionList and DropPartitionList are arrays of strings in which each string represents a partition mask. The eID update manager <b>230</b> remembers the new accept partition list and uses the list to filter incoming operations. The eID update manager <b>230</b> may then walk the data store to remove items whose hashed eID matches the patterns in the drop partition list. Either the accept partition list or the drop partition list may be empty. When a storage node boots, its accept partition list may be empty, and may be initialized using this call from the partition manager <b>232</b>. <ul id="ul0029" list-style="none"><li id="ul0029-0001" num="0300"> empty(subscriber identifier, bucket identifier) </li></ul>

0301This callback indicates that the specified bucket has become empty locally, and that the partition manager <b>232</b> should thus consider merging or deleting it. <ul id="ul0030" list-style="none"><li id="ul0030-0001" num="0302"> hint(subscriber identifier, bucket identifier, mask) </li></ul>

0303This peer-to-peer call may serve as a hint that another storage node should consider joining the named partition.

0304In one embodiment, the partition manager <b>232</b> may be a client of the group health <b>226</b> component for determining the load of nodes within replication groups through an API to the group membership and health <b>226</b> component. In one embodiment, the partition manager <b>232</b> may also query the storage node locator <b>216</b> to look for underutilized storage nodes.

0305In one embodiment, the splitting and merging of partitions may be driven only by stress on disk storage. In particular, once local disk usage gets beyond a certain threshold, locally-hosted partitions may be split. Other embodiments may use other architectures and mechanisms for dividing entities among a set of available hosts. For example, in one embodiment, consistent hashing (or Distributed Hash Tables (DHTs)) may be used to spread entity replicas semi-randomly among the available hosts. This embodiment may make adding or deleting hosts in the system relatively simple, but may tend to make querying inefficient, as queries may need to be sent to almost all hosts serving the bucket. Therefore, scaling the query-processing power for a bucket would be difficult in this embodiment. In another exemplary embodiment, entities may be distributed based upon their attributes, but note that this embodiment may make query planning and execution more complex. This embodiment may also increase the complexity of adding and removing hosts, and may make it more difficult to react to changing data distributions.

0000Storage Nodes

0306<figref idref="DRAWINGS">FIG. 11</figref> illustrates an exemplary storage node and its components according to one embodiment. Note that the partition manager <b>232</b> and associated components were described above in the section titled <i>Partition Manager</i>, and the local query processor <b>228</b> is further described below in the section titled <i>Query Service</i>. The following description of <figref idref="DRAWINGS">FIG. 11</figref> focuses on the eID, store <b>236</b> and its associated components: the eID update manager <b>276</b> and the query indexes <b>234</b> compiled on the eID store <b>236</b>. Also note that, in one embodiment, instances of the illustrated components may reside on every storage node <b>270</b> in a searchable data service implementation.

0307In one embodiment, a local eID store <b>236</b> and a local eID update manager <b>230</b> may function together to provide one or more of, but not limited to, the following functionalities: <ul id="ul0031" list-style="none"><li id="ul0031-0001" num="0308"> Support a list attributes API: After clients submit updates, the clients may read back the attributes associated with eIDs. </li><li id="ul0031-0002" num="0309"> Support creation and re-creation of query indexes <b>234</b>: The eID store <b>236</b> may be used as an authoritative store for creation of query indexes <b>274</b>. If these indexes <b>234</b> are lost, they may be regenerated using the local eID store <b>236</b>. </li><li id="ul0031-0003" num="0310"> Support query subsystem <b>204</b> requirement for a chunk request whereby a list of eIDs is submitted for which the attributes for each are to be returned. </li></ul>

0311In one embodiment, the instances of an eID store <b>236</b> on the various storage nodes <b>270</b> within a searchable data service implementation may collectively provide one or more of, but not limited to, the following functionalities: <ul id="ul0032" list-style="none"><li id="ul0032-0001" num="0312"> Durability: When a client is told that an update has been accepted, the client may require a high level of confidence that the replicated eID store <b>236</b> will not lose the data. </li><li id="ul0032-0002" num="0313"> Consistency: Replicas exhibit eventual consistency within a specified Service Level Agreement (SLA) with a customer. </li><li id="ul0032-0003" num="0314"> Reliability, availability, scalability: a searchable data service implementation may be required to support these as needed to enable the overall system to meet particular SLAs. </li></ul>

0315In one embodiment, to provide the durability and consistency functionalities, the instances of eID store <b>236</b> may communicate using a gossip mechanism, as further described later in this document. The partition manager <b>232</b>, through interactions with the group health <b>226</b> component and a stress manager component, may manage the disk usage of the eID stores <b>236</b> through dynamic partitioning, and durability of the eID stores <b>236</b> through new replica creation when nodes fail.

0000eID Update Manager

0316In one embodiment, the eID update manager <b>230</b> may receive updates and list-attribute requests, for example via TCP, on a specified port. The eID update manager <b>230</b> may also communicate with its local partition manager <b>232</b> to report problems and status, and to directions on which bucket partitions <b>254</b> the eID update manager <b>230</b> should maintain, and which it should get rid of, if any.

0317Note that a storage node <b>270</b> may include one or more bucket partitions <b>254</b>. In one embodiment, partitioning decisions are outside the scope of the eID update manager <b>230</b>. However, the eID update manager <b>230</b> is informed of partitioning decisions and abides by them.

0000eID Store

0318In one embodiment, the eID store <b>236</b> may be implemented as a Berkeley database (BDB).

0319Note that other embodiments may use other mechanisms to implement the eID store <b>236</b>. A BDB provides the capacity to find all the attributes given a subscriber identifier, a bucket identifier, and an entity identifier (eID) within it. A BDB stores information as key-value pairs; the key may be referred to herein as a BDB-key, and the value as BDB-value. In one embodiment, the BDB-key and BDB-value may be formed as follows: <ul id="ul0033" list-style="none"><li id="ul0033-0001" num="0320"> BDB-key=Key(subscriber identifier, bucket identifier, eID) </li><li id="ul0033-0002" num="0321"> BDB-value={updates-for-the-eID-above}</li></ul>

0322Key(subscriber identifier, bucket identifier, eID) is a function that forms a unique key using the specified arguments. For example, in one embodiment, this function may form the BDB-key by concatenating the subscriber identifier, the bucket identifier, and the eID strings. Continuing the example, to list all eIDs given a bucket identifier, the function may prefix the concatenated subscriber identifier, bucket identifier, and eID strings with some delimiting information. For example, a BDB-key may be formed as “p12_client1bucket1/photos/xy.jpg”, which indicates that the subscriber identifier (“client1”) concatenated with one of the subscriber's buckets (“bucket1”) is 12 characters long, and whatever follows after 12 characters is the eID string: “/photos/xy.jpg”. Depending on which lookup functionalities are desired (equality lookup on subscriber identifier, bucket identifier, and eID; equality lookup on subscriber identifier and bucket but range and equality lookup for eID; etc.), the Key( . . . ) may be implemented in various ways in embodiments.

0323In one embodiment, the BDB-value may include a collection of update operations (e.g., replace, add, and/or delete) and their corresponding sequenceIDs that help make up the attributes for the eID in the BDB-key. In one embodiment, a new update operation on an attribute supercedes an existing update operation in the eID store if its sequence ID is higher. For example, given an eID, a replace operation on an attribute with a sequence ID higher than a replace on that attribute in the eID store <b>236</b> removes the latter from the eID store <b>236</b>. As another example, an overall delete operation with a certain sequence ID makes all update operations with lower sequence IDs irrelevant.

0324To illustrate the above, consider the following exemplary BDB-value at a particular eID: <tables id="TABLE-US-00004" num="4"><table frame="none" colsep="0" rowsep="0" pgwide="1"><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="259PT" align="left" /><thead><row><entry /></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry>{ (op=replace, name=n1, value=v1, ts=t1), (op=replace, name=n2, value=v2, ts=t2),</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="245PT" align="left" /><tbody valign="top"><row><entry /><entry>(op=add,name=n2,value=v3,ts=t3)}</entry></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables><br /> where op indicates operation and ts indicates a sequence ID. Assume for this example that t<b>4</b>>t<b>3</b>>t<b>2</b>>t<b>1</b>. At “this moment” in the example, the attributes implied by the BDB-value are: <ul id="ul0034" list-style="none"><li id="ul0034-0001" num="0325"> {(n<b>1</b>,v<b>1</b>,),(n<b>2</b>,v<b>2</b>),(n<b>2</b>,v<b>3</b>)} <br /> where n<b>2</b> is multiple-valued. Now consider updates via one of the following exemplary scenarios at the same eID: <br /> First Scenario </li><li id="ul0034-0002" num="0326"> (op=replace, name=n<b>2</b>, value=v<b>4</b>, ts=t<b>4</b>) <br /> This causes the BDB-value to contain: </li><li id="ul0034-0003" num="0327"> {(op=replace, name=n<b>1</b>, value=v<b>1</b>, ts=t<b>1</b>), (op=replace, name=n<b>2</b>, value=v<b>4</b>, ts=t<b>4</b>)} <br /> Thus: </li><li id="ul0034-0004" num="0328"> (op=replace, name=n<b>2</b>, value=v<b>2</b>, ts=t<b>2</b>), (op=add,name=n<b>2</b>,value=v<b>3</b>,ts=t<b>3</b>) <br /> are jettisoned from the list of updates, as they are superceded by the new update. <br /> Second Scenario </li><li id="ul0034-0005" num="0329"> (op=delete, ts=t<b>4</b>) <br /> This causes the BDB=value to contain only: </li><li id="ul0034-0006" num="0330"> {(op=delete, ts=t<b>4</b>)} <br /> All of the other operations are removed, as they are all superceded by this new operation. <br /> Third Scenario </li><li id="ul0034-0007" num="0331"> (op=add, name=n<b>1</b>, value=v<b>5</b>, ts=t<b>4</b>) </li></ul>

0332This causes the BDB-value to contain: <tables id="TABLE-US-00005" num="5"><table frame="none" colsep="0" rowsep="0" pgwide="1"><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="259PT" align="left" /><thead><row><entry /></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry>{ (op=replace, name=n1, value=v1, ts=t1), (op=add, name=n1, value=v5, ts=t4),</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="245PT" align="left" /><tbody valign="top"><row><entry /><entry>(op=replace, name=n2, value=v2, ts=t2), (op=add,name=n2,value=v3,ts=t3) }</entry></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables><br /> In this scenario, no update needs to be thrown out. Two attributes, n<b>1</b> and n<b>2</b>, are multi-valued. <br /> Query Indexes

0333In one embodiment, the query indexes <b>234</b> may be implemented as a Berkeley database (BDB). Note that other embodiments may use other mechanisms to implement the query indexes <b>234</b>. In one embodiment, given a bucket <b>252</b>, the query indexes <b>234</b> allow a mapping from {name, value} pairs to eIDs. Thus, for query indexes <b>234</b>: <tables id="TABLE-US-00006" num="6"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="217PT" align="left" /><thead><row><entry /></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry>BDB-key = Key( subscriber identifier, bucket identifier, name, value )</entry></row><row><entry>BDB-value = { all-eIDs-with-{name, value}-above }</entry></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0334One embodiment may perform equality lookups with subscriber identifier, bucket identifier, and name, and equality and range lookups with the value. In one embodiment, the Key(subscriber identifier, bucket identifier, name, value) function for the query indexes <b>234</b>, given the exemplary query: <ul id="ul0035" list-style="none"><li id="ul0035-0001" num="0335"> @name=“some-name”, @value>“string1” AND @value<“string2”</li></ul>

0336may support the query by allowing the following translation: <tables id="TABLE-US-00007" num="7"><table frame="none" colsep="0" rowsep="0" pgwide="1"><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="280PT" align="left" /><thead><row><entry /></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry>BDB-Key > Key ( subscriber identifier, bucket identifier, “some-name”, “string1” ) AND BDB-</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="266PT" align="left" /><tbody valign="top"><row><entry /><entry>Key < Key ( subscriber identifier, bucket identifier, “some-name”, “string2” )</entry></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0337Some exemplary methods to implement the function Key( . . . ) were discussed under the section titled <i>eID Store </i>above, and are intended to apply here as well.

0338In one embodiment, the BDB-value for the query indexes <b>234</b> is a set of update operations (e.g., add and/or replace), along with their sequence IDs that associate a set of one or more eIDs with the {name, value} pair in the BDB-key. Note that every new update of the eID store <b>236</b> may cause one or more previous updates to become irrelevant. The query indexes <b>234</b> need to receive the new update, as well as all updates that it supercedes.

0000Storage Node Use Cases

0339The following describes several exemplary searchable data service storage node use cases according to one embodiment. The first two use cases (processing update requests and processing list-attribute requests) describe the processing of external events. The rest describe the processing of internal events.

0340The following describes the processing of update requests according to one embodiment. Upon receiving an update request from a request router <b>202</b>, if the eID update manager <b>230</b> determines that the update is not for buckets it currently maintains, an error is returned. If the eID update manager <b>230</b> determines that the update is marked by the request router <b>202</b> with a sequence ID that is more than T (e.g., ˜5-10) seconds in the future, the eID update manager <b>230</b> returns an error. In one embodiment, the eID update manager <b>230</b> may also check its NTP synchronization status and raise an alarm, if necessary.

0341In one embodiment, the eID update manager <b>230</b> may “gcast” the update using the group communication <b>222</b> component. The number of bytes sent across the network may be approximated (see the <i>Group Communications </i>section for more details); typically, the number of bytes may be N times the size in bytes of the update message, where N is the number of replicas needed for durability. The gcast may return a node set to which the update may be written for durability, or may time out.

0342The eID update manager <b>230</b> performs a read-modify-write of the eID store <b>236</b> with the updates. This may cause some updates to be superceded, and new updates to be entered. If the eID update manager <b>230</b> finds that the update cannot be applied because it has been superceded, an indication that the message is late is returned. The eID update manager <b>230</b> logs the new update, and the superceded updates, in a durable log. If the eID update manager <b>230</b> successfully gcasts, updates the eID store <b>236</b>, and writes to its log, it returns the node-set obtained from gcast. Otherwise, an error may be returned.

0343The following describes the processing of list-attribute requests according to one embodiment. The eID update manager <b>230</b> reads its local eID store <b>236</b> to find the eID specified by the request. If the eID is found, its attributes are read and a successful response sent back. If the eID is not found, an error may be returned.

0000Processing Internal Events

0344If the eID store log changes, a query index updater may read the new additions and updates the query index <b>234</b>. An anti-entropy daemon reads the new additions and updates its a data structure (e.g., a Merkle tree) for anti-entropy.

0345The following describes the processing of an apply message call made by the group communication <b>222</b> component according to one embodiment. If the eID update manager <b>230</b> determines that the update is not for buckets it currently maintains, an error is returned. If the eID update manager <b>230</b> determines that the update is marked by the request router <b>202</b> with a sequence ID that is more than T (e.g., ˜5-10) seconds in the future, the message is accepted, and the eID update manager <b>230</b> checks its NTP synchronization status and raises an alarm, if necessary.

0346The eID update manager <b>230</b> performs a read-modify-write of the eID store <b>236</b> with the update message. This may cause some updates to be superceded, and new updates to be entered. If the eID update manager <b>230</b> finds that the update cannot be applied because it has been superceded, an indication that the message is late is returned. If the eID update manager <b>230</b> finds that the update has already been applied, an indication that the message is a duplicate is returned. The eID update manager <b>230</b> logs the new update, and the superceded updates, in a durable log. If the eID update manager <b>230</b> successfully updates the eID store <b>236</b> and writes to its log, it returns OK (successful). Otherwise, an error may be returned.

0347The following describes the processing of an anti-entropy call made by the group communication <b>222</b> component according to one embodiment. In response to the call, an anti-entropy daemon connects to the indicated host and carries out an anti-entropy session with the host. Anti-entropy is further discussed elsewhere in this document.

0348The following describes the processing of a set partitions call made by the partition manager <b>232</b> according to one embodiment. The eID update manager <b>230</b> writes its log with the new accept list and drop list. The eID update manager <b>230</b> starts a cleaner thread with the drop list to prune itself of eIDs that it is no longer responsible for. The query index <b>234</b> starts its own cleaner thread when it reads the logged event. An anti-entropy daemon also starts its own cleaner thread when it reads the logged event.

0000eID Update Manager Interfaces

0349The following describes exemplary interfaces that may be exposed or expected by an eID update manager <b>230</b> according to one embodiment. Note that these interfaces are exemplary, and are not intended to be limiting.

0350The eID update manager <b>230</b> may expose one or more of, but not limited to, the following interfaces to the request router <b>202</b>: <tables id="TABLE-US-00008" num="8"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="203PT" align="left" /><thead><row><entry /><entry /></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry /><entry>replace ( bucket identifier, eID, name, value, prev-seq-ID) OR</entry></row><row><entry /><entry>add( buc ket identifier, eID, name, value, prev-seq-ID) OR</entry></row><row><entry /><entry>delete ( bucket identifier, eID, name, value, prev-seq-ID)</entry></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0351The eID update manager <b>230</b> may expose one or more of, but not limited to, the following interfaces to a local group communication <b>222</b> component: <tables id="TABLE-US-00009" num="9"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="42PT" align="left" /><colspec colname="1" colwidth="175PT" align="left" /><thead><row><entry /><entry /></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry /><entry>apply(Group, Msg) --> ok|dup|late|error</entry></row><row><entry /><entry>antientropy(Group, Host, Cookie) --> Status</entry></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0352The eID update manager <b>230</b> may expose, but is not limited to, the following interface to a local partition manager <b>232</b>: <ul id="ul0036" list-style="none"><li id="ul0036-0001" num="0353"> setpartitions(Subscriber, Bucket, AcceptPartitionList, DropPartitionList) <br /> Note that AcceptPartitionList and DropPartitionList are lists of {mask, value} pairs. </li></ul>

0354The eID update manager <b>230</b> may expect one or more of, but not limited to, the following interfaces from a local group communication <b>222</b> component: <tables id="TABLE-US-00010" num="10"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="28PT" align="left" /><colspec colname="1" colwidth="189PT" align="left" /><thead><row><entry /><entry /></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry /><entry>gcast(Group, Msg) --> {ok, Hosts, Cookie} | error</entry></row><row><entry /><entry>gsync(Cookie, Timeout)--> true|false</entry></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0355The eID update manager <b>230</b> may expose, but is not limited to, the following interface from a local partition manager <b>232</b>: <ul id="ul0037" list-style="none"><li id="ul0037-0001" num="0356"> empty(Subscriber, Bucket) <br /> Query Service </li></ul>

0357In one embodiment, the query subsystem <b>204</b>, or query service, of a searchable data service system may provide one or more interfaces for parsing client queries, retrieving data, and correlating query results sets. In one embodiment, the query service may involve or include several components of the searchable data service as illustrated in <figref idref="DRAWINGS">FIG. 6</figref>, including, but not limited to, one or more query TSARs <b>212</b>, query caches <b>214</b>, query node locators <b>220</b>, and, on each storage node <b>270</b>, a local query processor <b>228</b>, local query index store <b>234</b>, and entity ID (eID) store <b>236</b>. Note that these components may be referred to using different numbers in the following Figures.

0358<figref idref="DRAWINGS">FIG. 12</figref> illustrates various components of the searchable data service that may constitute or interact with the query subsystem to perform the servicing of queries from clients of the searchable data service, and further illustrates the data flow among the components, according to one embodiment. The query subsystem may provide efficient execution of a client-submitted query against all storage nodes <b>370</b> in the searchable data service containing the relevant entity IDs (eIDs) (belonging to a particular bucket), aggregating the results from each individual storage node <b>370</b>, and caching eID sets satisfying each given query. In one embodiment, to perform the processing of queries, the query subsystem may include, but is not limited to the following components: <ul id="ul0038" list-style="none"><li id="ul0038-0001" num="0359"> query node locator <b>354</b> may make routing decisions for each particular query. In one embodiment, repeated client queries may be encouraged to route the same path through the-query system in order to maximize the benefits of query cache <b>364</b>. </li><li id="ul0038-0002" num="0360"> query TSAR (Top Search AggregatoR) <b>360</b> may distribute a query to the appropriate set of storage nodes <b>370</b> for a given bucket, as well as aggregating results and query caching. </li><li id="ul0038-0003" num="0361"> local query execution engines <b>376</b>, one on each storage node <b>370</b>, are responsible for executing the query locally on each of the storage nodes <b>370</b>. </li></ul>

0362In one embodiment, query TSARs <b>360</b> are essential treated as equals. Each query TSAR <b>360</b> may answer any client query. This may help to simplify the addition and removal of individual nodes. However, since query results may be cached in query caches <b>364</b> on the individual nodes, one embodiment may attempt to route identical queries for the same storage domain through the same query TSAR <b>360</b> nodes as often as possible. To help in routing queries through query TSARs <b>360</b>, the request router <b>352</b> may access the query node locator <b>354</b> service to obtain lists of query nodes for specified buckets.

0363In addition to the abovementioned services and components, one or more other components or services may be accessed by the query service. For example, the storage node locator service <b>369</b> may be accessed to locate a set or list of appropriate storage nodes <b>370</b> for a given bucket. As another example, the query service may leverage or participate in the overall system node health service (group membership and health <b>226</b>, in <figref idref="DRAWINGS">FIG. 6</figref>), which may monitor various nodes joining and leaving the system, and may propagate that health information to other nodes in the system.

0000Query Node Locator

0364In order for query caching to provide a beneficial hit rate, one embodiment may attempt to ensure that the same client queries are routed by the coordination service (request router <b>352</b>) to the same query TSAR <b>360</b> nodes, if possible. In one embodiment, a query node locator <b>354</b>, one of which may be instantiated in each coordinator node <b>350</b>, may encapsulate the logic for providing that routing. In one embodiment, query node locator <b>354</b> may implement a consistent hashing scheme that allows for the random distribution of the incoming queries over the set of participating nodes. Other embodiments may implement other random or non-random mechanisms for distributing queries.

0365In one embodiment, the query node locator <b>354</b> implements a consistent hash function to assign each node and key an m-bit identifier using a base hash function, such as SHA-1. In one embodiment, a node's identifier may be chosen by hashing the node's IP address, while a key identifier may be generated by hashing the combination of the domain and the normalized query string. The term “key” may be used to refer to both the original key and its image under the hash function, as the meaning will be clear from the context in which the term is used. Similarly, the term “node” may be used to refer to both the node and its identifier under the hash function. In one embodiment, the identifier length may be large enough to make the probability of two nodes or keys hashing to the same identifier negligible.

0366In one embodiment, the hashmap structure used by query node locator <b>354</b> may include one or more of, but is not limited to, the following fields: <ul id="ul0039" list-style="none"><li id="ul0039-0001" num="0367"> key—a hash of the combined domain (bucket) name and query string expression. value—a set of eIDs satisfying a query expression for the given bucket. </li><li id="ul0039-0002" num="0368"> cost—the time it took to originally execute the query expression; may be used, for example, in garbage collection and replacement algorithms. </li><li id="ul0039-0003" num="0369"> timestamp—the local time when the entry was inserted in the cache; may be used, for example, in garbage collection and validation algorithms. </li></ul>

0370Consistent hashing may assign keys to nodes as follows. Identifiers are ordered in an identifier circle modulo 2^m. Key k is assigned to the first node whose identifier is equal to or follows (the identifier of) k in the identifier space. This node is called the successor node of key k, denoted by successor(k). If identifiers are represented as a circle of numbers from 0 to 2^m−1, then successor(k) is the first node clockwise from k.

0371<figref idref="DRAWINGS">FIG. 13</figref> illustrates an identifier circle with m=3. The circle has three nodes: 0, 1, and 3. The successor of identifier <b>1</b> is node <b>1</b>, so key <b>1</b> would be located at node <b>1</b>. Similarly, key <b>2</b> would be located at node <b>3</b>, and key <b>6</b> at node <b>0</b>.

0372Consistent hashing may allow nodes to enter and leave the searchable data service with minimal disruption. To maintain the consistent hashing mapping when a node n joins the network, certain keys previously assigned to node n's successor now become assigned to node n. When node n leaves the network, all of its assigned keys are reassigned to node n's successor. No other changes in assignment of keys to nodes need occur. In the example given in <figref idref="DRAWINGS">FIG. 13</figref>, if a node were to join with identifier <b>7</b>, it would capture the key with identifier <b>6</b> from the node with identifier <b>0</b>.

0000Query TSAR (Top Search AggregatoR)

0373In one embodiment, query processor <b>362</b> is the first component of the searchable data service system that deals with the query expression provided by the client <b>330</b> in the query message. Query processor <b>362</b> may preprocess the query expression. In an embodiment that allows for unnormalized syntax in the query language, an initial step that the query processor <b>362</b> performs is to transform the query into its canonical, normalized form. In one embodiment, query processor <b>362</b> may also reorder the predicates in a query expression to normalize them so that semantically identical queries look the same. For example, the query expression: <ul id="ul0040" list-style="none"><li id="ul0040-0001" num="0374"> [predicate <b>1</b>] AND [predicate<b>2</b>] AND [predicate<b>3</b>] <br /> should be represented by the same normalized query expression as the query expression: </li><li id="ul0040-0002" num="0375"> [predicates] AND [predicate <b>1</b>] AND [predicate<b>2</b>] <br /> This normalization of predicates in query expressions may, for example, help in allowing the system to achieve a higher query cache <b>364</b> hit rate. </li></ul>

0376Following the preprocessing of the query expression, query processor <b>362</b> may check its local query cache <b>364</b> to determine if the query cache <b>364</b> contains the necessary result set to satisfy the given (possibly normalized) query expression. If query cache <b>364</b> does contain the result set, the result set is retrieved from the query cache <b>364</b> and returned to the client <b>330</b> via coordinator node <b>350</b>. Otherwise, the query expression is passed along to the query aggregator <b>366</b>, which is responsible for retrieving the result set from the corresponding storage nodes <b>370</b>. After the result set is retrieved from the storage nodes <b>370</b>, it is cached in the local query cache <b>364</b> and returned to the client <b>330</b> via coordinator node <b>350</b>.

0377The efficiency of query caching in query cache <b>364</b> may be a performance parameter that affects the overall performance of the searchable data service system. Overall performance of the system may be improved by resolving hot queries against the query cache <b>364</b> without having to go to the individual storage nodes <b>370</b> to retrieve the results sets.

0000Query Aggregator

0378In one embodiment, query aggregator <b>366</b> may use the storage node locator <b>368</b> service in order to locate a set of storage nodes <b>370</b> that contain eIDs for the bucket on which the current query is executed. After the set of storage nodes <b>370</b> is determined, query aggregator <b>366</b> may send the query request to the local query execution engines <b>376</b> on the each of the storage nodes <b>370</b>, retrying if necessary. After the result sets are received from all the storage nodes <b>370</b> participating in the query, the result sets may be merged into a single set based on the sorting attribute, if necessary.

0000Local Query Execution Engine

0379<figref idref="DRAWINGS">FIG. 14</figref> illustrates an exemplary architecture for a single storage node <b>370</b> according to one embodiment. Local query execution engine <b>376</b> may be closely tied to the storage node <b>370</b>'s eID store <b>380</b> and local query index store <b>378</b>. Local query execution engine <b>376</b> executes queries locally against the set of eIDs stored on this particular storage node <b>370</b>. Since all the information about the eIDs is present locally, local query execution engine <b>376</b> may locally (i.e., within this storage node <b>370</b>) execute the provided query <b>390</b>, sort the results, and return the query result set <b>390</b> (along with the sorting attribute) to the query TSAR <b>360</b>. In one embodiment, an incoming query <b>390</b> may be locally parsed by a parser <b>372</b> and optimized by a query optimizer <b>374</b> prior to being executed against the eID store <b>380</b> by the local query execution engine <b>376</b>. In one embodiment, parser <b>372</b>, query optimizer <b>374</b>, and local query execution engine <b>376</b> may be components of a local query processor <b>228</b>, as illustrated in <figref idref="DRAWINGS">FIG. 6</figref>.

0000Query Syntax and Search Expressions

0380In embodiments, an exemplary query message may include one or more of, but is not limited to, the following fields: <ul id="ul0041" list-style="none"><li id="ul0041-0001" num="0381"> Subscriber identifier—an identifier for the particular client or client of the searchable data service. </li><li id="ul0041-0002" num="0382"> Bucket identifier—identifies a bucket that defines the limits of data that may be considered in the query. </li><li id="ul0041-0003" num="0383"> Node ID—a node identifier. </li><li id="ul0041-0004" num="0384"> Query expression—a search expression to be applied for this query. </li><li id="ul0041-0005" num="0385"> “More Tokens”—an opaque moreToken object may be returned to the client when the number of eIDs satisfying the query expression exceeds a pagination limit. This token may be resubmitted with the same query in order to retrieve the next set of results (eIDs). </li><li id="ul0041-0006" num="0386"> Sequencing token. </li></ul>

0387In embodiments, the query service may support one or more of, but not limited to, the following types of operations for queries to the searchable data service by clients of the service: <ul id="ul0042" list-style="none"><li id="ul0042-0001" num="0388"> Boolean operations (e.g.: AND, OR, NOT, etc.) </li><li id="ul0042-0002" num="0389"> Arithmetic operations (e.g.: <,>, <=, >=, <>, =, !=) </li><li id="ul0042-0003" num="0390"> String comparision operations (e.g.: prefix, “contains”, etc.) </li><li id="ul0042-0004" num="0391"> Sorting of the results set of entities based on a client-specified attribute. In one embodiment, sorting may be allowed on a single attribute only. Other embodiments may allow sorting on two or more attributes. </li><li id="ul0042-0005" num="0392"> Pagination of the results set. </li></ul>

0393In one embodiment, search expressions in the searchable data service may represent a subset of XPath, a W3C recommendation. Note that other embodiments may use other protocols for search expressions. In one embodiment, a relatively small subset of XPath syntax may be used, given that attributes are lists of (name,value) pairs, and multiple levels in a markup language (e.g., XML) document are not allowed. Note that other embodiments may allow multiple levels in a markup language document. Also note that other embodiments may use relatively larger subsets of Xpath syntax. Therefore, the query syntax that is used in at least some embodiments of a searchable data service relates to the predicate test expressions of XPath definition.

0394In some embodiments, in addition to an Xpath query syntax, one or more unnormalized forms for search expressions—expressions with implicit syntax that may be reduced to a canonical form in accordance with one or more normalization rules—may be allowed. Allowing unnormalized forms for search expressions may help provide flexibility in testing and implementation for developers utilizing the searchable data service.

0395In embodiments, search expressions work on the attribute lists of objects; that is, a truth value may be calculated using one or more of, or all, of the attributes of an object and, if TRUE, the object may be selected.

0396The following are some examples of search expressions according to one embodiment, and are not intended to be limiting. <ul id="ul0043" list-style="none"><li id="ul0043-0001" num="0397"> [@name=“xxxxxx” starts-with (@value=“yyyyyy”)]</li></ul>

0398This expression refers to a test to be applied to every {name, value} pair of the attribute list. The square brackets “[]” designate an individual element test). After the application of this test, a small set of {name, value} pairs that matched the expression are left. This set is referred to as a “node set” by XPath. If a non-null node set for an object is obtained, its key will be selected. <tables id="TABLE-US-00011" num="11"><table frame="none" colsep="0" rowsep="0" pgwide="1"><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="273PT" align="left" /><thead><row><entry /></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry>[ @name = “prefix” @value = “keyword”] AND [@name = “glassy” starts-with (@value =</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="259PT" align="left" /><tbody valign="top"><row><entry /><entry>“tasty”)]</entry></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0399In this example, two node sets are combined. As indicated in XPath, a node set evaluates to TRUE if and only if it is not a null set. In the above example, two node sets are computed separately with the attribute-list of an object, and their truth values are combined using AND.

0400Note that [@value=“foo”] does not mean the same as NOT[@value!=“foo”]; the former is true if and only if some attribute has value with the string-value “foo”; the latter is true if and only if all attributes have value with the string-value “foo”.

0401The following is a summary of an exemplary query syntax that is allowed in search expressions in one embodiment. Note that other embodiments may not include at least part of this syntax and/or may include other syntax: <tables id="TABLE-US-00012" num="12"><table frame="none" colsep="0" rowsep="0" pgwide="1"><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="266PT" align="left" /><thead><row><entry /></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry>query expression &lt;− (predicate expression)?</entry></row><row><entry>predicate expression &lt;− predicate | NOT predicate expression | predicate expression AND</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="252PT" align="left" /><tbody valign="top"><row><entry /><entry>predicate expression | predicate expression OR predicate expression | predicate</entry></row><row><entry /><entry>expression sort expression</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="266PT" align="left" /><tbody valign="top"><row><entry>sort expression &lt;− ‘SORTBY[“ attribute name ’]“ | ‘SORTBY[‘ attribute name ’ ASC]’ |</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="252PT" align="left" /><tbody valign="top"><row><entry /><entry>‘SORTBY[‘ attribute name ’ DESC]’</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="266PT" align="left" /><tbody valign="top"><row><entry>predicate &lt;− ‘[‘ attribute name ’]’ | ‘[‘ attribute name _value test expression_’]’</entry></row><row><entry>attribute name &lt;− ‘@name =’ attribute</entry></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0402In the above, attribute is a string name of a given attribute in the system. <tables id="TABLE-US-00013" num="13"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="217PT" align="left" /><thead><row><entry /></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry>value test expression <− value test | NOT value test expression | value</entry></row><row><entry>test expression AND</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="203PT" align="left" /><tbody valign="top"><row><entry /><entry>value test expression | value test expression OR value test expression</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="217PT" align="left" /><tbody valign="top"><row><entry>value test <− ‘@value =’ test value</entry></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables><br /> In the above, value has to be equal to test value. <ul id="ul0044" list-style="none"><li id="ul0044-0001" num="0403"> value test <- ‘@value !=’ test value <br /> In the above, value has to be not equal to test value. </li><li id="ul0044-0002" num="0404"> value test <- ‘@value >’ test value <br /> In the above, value has to be greater than test value. </li><li id="ul0044-0003" num="0405"> value test <- ‘@value >=’ test value <br /> In the above, value has to be greater than or equal to test value. </li><li id="ul0044-0004" num="0406"> value test <- ‘@value <’ test value <br /> In the above, value has to be less than test value. </li><li id="ul0044-0005" num="0407"> value test <- ‘@value <=’ test value <br /> In the above, value has to be less than or equal to test value. </li><li id="ul0044-0006" num="0408"> value test <- ‘startsWith(@value=’ test value ‘)’ <br /> In the above, value has to start with test value. </li><li id="ul0044-0007" num="0409"> value test <- ‘contains(@value=’ test value ‘)’ <br /> In the above, value contains test value as a substring. </li></ul>

0410The following is a summary of exemplary query syntax rules for search expressions in one embodiment. Note that other embodiments may not include at least part of these syntax rules and/or may include other syntax rules or modifications of these rules: <ul id="ul0045" list-style="none"><li id="ul0045-0001" num="0411"> A Boolean test to be carried out on every {name, value} pair of an object's attribute list is enclosed within a square bracket [. . . ]. </li><li id="ul0045-0002" num="0412"> Within the square brackets, the name and value parts of a {name, value} pair are referred to using “@name” and “@value” on the left-hand side. </li><li id="ul0045-0003" num="0413"> The first part of an expression must be the name of the attribute in the form of “@name=”, and may be followed by zero or more Boolean tests of attribute value. </li><li id="ul0045-0004" num="0414"> The operators “> >=< <== !=” may be used as comparison operators with a string on the right-hand side. </li><li id="ul0045-0005" num="0415"> String functions “starts-with” and “contains” from XPath may be used for string value attributes. </li><li id="ul0045-0006" num="0416"> All @name parts of an attribute are considered strings, the @value parts are also considered strings. </li><li id="ul0045-0007" num="0417"> operators are AND, OR, and NOT. These may be used to combine tests on a {name, value} pair. </li><li id="ul0045-0008" num="0418"> Attribute sets obtained using tests within [. . . ] have truth values as given by XPath (Booolean function of node-sets) and hence can be combined using Boolean operators. </li><li id="ul0045-0009" num="0419"> An optional SORTBY expression may specify the attribute on which the result set should be sorted. SORTBY expression may include ASC (ascending) and DESC (descending) specifiers to indicate the sort order. ASC (ascending) is the default sort order. </li></ul>

0420The following is an exemplary search expression according to the exemplary canonical search expression syntax as described above: <tables id="TABLE-US-00014" num="14"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="217PT" align="left" /><thead><row><entry /></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry>[@name = ″lastName″ starts-with (@value = “Adams”)] AND</entry></row><row><entry>[@name = ″firstName″ @value</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="203PT" align="left" /><tbody valign="top"><row><entry /><entry>= ″John″] AND [@name = ″age″ @value > ″25″ AND @value <</entry></row><row><entry /><entry>″60″] SORTBY[@name =</entry></row><row><entry /><entry>″year″ DESC]</entry></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables><br /> Unnormalized Search Expressions

0421The above describes an exemplary canonical search expression syntax using Xpath syntax that may be used in embodiments of the searchable data service. Some embodiments of the searchable data service, however, may accept unnormalized search expressions with implicit syntax and reduce the statements to the canonical form using one or more normalization rules. The following presents examples of unnormalized search expressions and corresponding exemplary relevant normalization rules for reducing the implicit syntax to a canonical form. Note that the unnormalized expressions are shown on the left, with the normalized expressions on the right, as in: <ul id="ul0046" list-style="none"><li id="ul0046-0001" num="0422"> “unnormalized expression”=> [normalized expression]</li></ul>

0423A string, followed by comparison operators “> >=< <=: !=” MUST be followed by a string or a number; the expression will form a comparison-test: <tables id="TABLE-US-00015" num="15"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="28PT" align="left" /><colspec colname="1" colwidth="189PT" align="left" /><thead><row><entry /><entry /></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry /><entry>“index > 5” => [@name = ″index″ @value > ″5″]</entry></row><row><entry /><entry>“title:‘foo’” => [@name = ″title″ @value = ″foo″]</entry></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0424A negative-test is a test with “NOT” in front of it: <ul id="ul0047" list-style="none"><li id="ul0047-0001" num="0425"> “NOT keyword:‘xxxxxx’”=> [@name=“keyword” NOT(@value=“xxxxxx”)]</li></ul>

0426An element test is either a test or a negative-test as defined above. Element tests may be listed as a series connected by the Boolean operators AND or OR. If a Boolean operator is missing, it is assumed to be AND. Parentheses may be used to indicate the order in which the Boolean operators may be applied: <tables id="TABLE-US-00016" num="16"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="217PT" align="left" /><thead><row><entry /></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry>″title:‘foo’ NOT prefix:‘keyword’″ => [ @name = ″title″ @value =</entry></row><row><entry>″foo″] AND [ @name =</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="203PT" align="left" /><tbody valign="top"><row><entry /><entry>″prefix″ NOT (@value = ″keyword″) ]</entry></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0427A sequence of tests on the same attribute may be treated as belonging in the same predicate: <tables id="TABLE-US-00017" num="17"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="217PT" align="left" /><thead><row><entry /></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry>“price > 5 AND price < 20 AND available:‘yes’” => [ @name = “price”</entry></row><row><entry>@value > “5” AND</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="203PT" align="left" /><tbody valign="top"><row><entry /><entry>@value < “20” ] AND [ @name = “available” @value = “yes” ]</entry></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0428Sorting order may be specified by including “sortby” expression at the end of the query string, followed by the attribute name on which resulting set should be sorted. Additional modifier (“asc” or “desc”) may follow, specifying the sort order: <tables id="TABLE-US-00018" num="18"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="217PT" align="left" /><thead><row><entry /></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry>“year < 2010 AND author:‘John Doe’ sortby price desc” => [@name =</entry></row><row><entry>“year” @value <</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="203PT" align="left" /><tbody valign="top"><row><entry /><entry>“2010”] AND [@name = “author” @value = “John Doe”]</entry></row><row><entry /><entry>SORTBY[@name = “price”</entry></row><row><entry /><entry>DESC]</entry></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables><br /> Query Result Set

0429In one embodiment, queries submitted to the searchable data service may be processed by the query service of the searchable data service as described herein to generate one or more of, but not limited to, the following as part of the returned search results data: <ul id="ul0048" list-style="none"><li id="ul0048-0001" num="0430"> A set of one or more entity IDs (eIDs) that satisfy the query expression. In one embodiment, the number of eIDs that are returned may not exceed a predefined pagination limit. </li><li id="ul0048-0002" num="0431"> moreToken: an opaque object returned to the client when the number of eIDs satisfying the query expression exceeds a pagination limit. This token may be resubmitted with the same query in order to retrieve the next set of results (eIDs). <br /> Query Service Use Cases </li></ul>

0432The following describes several exemplary searchable data service query service use cases according to one embodiment. Note that these use cases may refer to the exemplary query subsystem architecture illustrated in <figref idref="DRAWINGS">FIG. 12</figref>.

0433The following describes the processing of an exemplary query request by the query service if all nodes are available, the query is not cached, and no sequencing token is provided, according to one embodiment. After receiving a query from a client <b>330</b>, request router <b>352</b> on a coordinator node <b>350</b> submits the query request, or query information from the query request, to the local query node locator <b>354</b>. Query node locator <b>354</b> may respond by returning a list of one or more query TSAR nodes <b>360</b>. In one embodiment, there may be a predefined limit on the number of query TSAR nodes <b>360</b> that may be returned in the list (e.g., the limit may be three). In one embodiment, the list of query TSAR nodes <b>360</b> may be ranked or sorted according to one or more criteria.

0434Request router <b>352</b> may then submit the query request to at least one query TSAR node <b>360</b> on the list received from the query node locator <b>354</b>. On a query TSAR node <b>360</b> that receives the query request from request router <b>352</b>, the local query processor <b>362</b> may submit the query request to a local query cache <b>364</b>. If the query cache <b>364</b> returns a negative cache hit result, the query TSAR node <b>360</b> may submit the query request to the local storage node locator <b>368</b>. The storage node locator <b>368</b> returns a set or list of storage nodes <b>370</b> that contain the bucket specified in the query request.

0435The query TSAR <b>360</b> may then submit the query request to one or more of the storage nodes <b>370</b> from the list returned by the storage node locator <b>368</b>. In one embodiment, the query request may be submitted to a minimal set of needed storage nodes <b>370</b>. The local query processor on each storage node <b>370</b> that receives the query request may process the query request against the local eID store and return a set of entity IDs (eIDs). In one embodiment, the set of eIDs may be limited by a page size (e.g., 100 entities). A “more token” indicator may be returned, if necessary, to indicate that there are more eIDs available to satisfy the query request.

0436The query TSAR <b>360</b> merges sets of eIDs received from the one or more storage nodes, if necessary, and submits the query request to the local query cache <b>364</b> to store the results. The query TSAR <b>360</b> then returns the query results to the request router <b>352</b>. Request router <b>352</b> then returns the query results to the requesting client <b>330</b>.

0437The following describes the processing of an exemplary query request by the query service if all nodes are available, the query is cached, and no sequencing token is provided, according to one embodiment. After receiving a query from a client <b>330</b>, request router <b>352</b> on a coordinator node <b>350</b> submits the query request, or query information from the query request, to the local query node locator <b>354</b>. Query node locator <b>354</b> responds by returning a list of one or more query TSAR nodes <b>360</b>. In one embodiment, there may be a predefined limit on the number of query TSAR nodes <b>360</b> that may be returned in the list (e.g., 3). In one embodiment, the list of query TSAR nodes <b>360</b> may be ranked or sorted according to one or more criteria.

0438Request router <b>352</b> then submits the query request to at least one query TSAR node <b>360</b> on the list received from the query node locator <b>354</b>. On a query TSAR node <b>360</b> that receives the query request from request router <b>352</b>, the local query processor <b>362</b> submits the query request to the local query cache <b>364</b>. If the query cache <b>364</b> returns a positive cache hit result, the query TSAR <b>360</b> returns the page of eIDs recovered from query cache <b>364</b> to the request router <b>352</b>. Rrequest router <b>352</b> then returns the query results to the requesting client <b>330</b>.

0439The following describes the processing of an exemplary query request by the query service if all nodes are available and a sequencing token is provided by the client, according to one embodiment. A sequencing token may be provided with the query request to help ensure that the searchable data service favors those storage nodes <b>370</b> specified in the node set of the sequencing token. By providing a sequencing token in a query request immediately following an update, a client <b>330</b> may significantly increase the chance of seeing the update reflected in the query result set. The two major differences from the exemplary use cases described above are that the query cache <b>364</b> is bypassed and that the process of selecting the storage nodes <b>370</b> to execute the query request against favors those storage nodes <b>370</b> indicated by the sequencing token.

0440After receiving a query from a client <b>330</b>, request router <b>352</b> on a coordinator node <b>350</b> submits the query request, or query information from the query request, to the local query node locator <b>354</b>. Query node locator <b>354</b> responds by returning a list of one or more query TSAR nodes <b>360</b>. In one embodiment, there may be a predefined limit on the number of query TSAR nodes <b>360</b> that may be returned in the list (e.g., 3). In one embodiment, the list of query TSAR nodes <b>360</b> may be ranked or sorted according to one or more criteria.

0441Request router <b>352</b> then submits the query request to at least one query TSAR node <b>360</b> on the list received from the query node locator <b>354</b>. The query TSAR <b>360</b> submits the request to the local storage node locator <b>368</b>. The storage node locator <b>368</b> returns a set or list of storage nodes <b>370</b> that contain the bucket specified in the query request. The query TSAR <b>360</b> uses the storage node <b>370</b> set specified in the sequencing token and the list of storage nodes <b>370</b> returned by the storage node locator <b>368</b> to determine a set of one or more storage nodes <b>370</b> to which the query request may be submitted, and then submits the query request to the determined storage node(s) <b>370</b>. The local query processor on each storage node <b>370</b> that receives the query request processes the query request against the local eID store and returns a set of entity IDs (eIDs). The query TSAR <b>360</b> merges sets of eIDs received from the storage nodes <b>370</b>, if necessary, and submits the query request to the local query cache <b>364</b> to store the results. The query TSAR <b>360</b> then returns the query results to the request router <b>352</b>. Request router <b>352</b> then returns the query results to the requesting client <b>330</b>.

0000Query Service Interfaces

0442The following describes exemplary interfaces that may be exposed or expected by components of the query service according to one embodiment. Note that these interfaces are exemplary, and are not intended to be limiting.

0443The following are exemplary exposed interfaces of components of the query service.

0444The query node locator <b>354</b> may be used to discover a ranked list of query TSAR <b>360</b> hosts. The query node locator <b>354</b> may expose at least the following exemplary interface: <ul id="ul0049" list-style="none"><li id="ul0049-0001" num="0445"> GetQueryNodes (subscriber identifier, bucket identifier, query-expression) </li></ul>

0446GetQueryNodes accepts a subscriber identifier, a bucket identifier, and a query expression, and returns a list of hosts that correspond to the provided information.

0447The query TSAR <b>360</b> may expose at least the following exemplary query interface: <ul id="ul0050" list-style="none"><li id="ul0050-0001" num="0448"> Query (queryID, subscriber identifier, bucket identifier, query-expression, more-token, update-cookie) </li></ul>

0449Query accepts a query ID, a subscriber identifier, a bucket identifier, a query expression, a more-token object and an update cookie. Query returns a query ID, an eID list, a more-token object, and/or an error message if appropriate.

0450The local query processor on each storage node <b>370</b> may expose at least the following exemplary query interface: <ul id="ul0051" list-style="none"><li id="ul0051-0001" num="0451"> Query (queryID, subscriber identifier, bucket identifier, query-expression, more-token, update-cookie) </li></ul>

0452Query accepts a query ID, a subscriber identifier, a bucket identifier, a query expression, a more-token object and an update cookie. Query returns a query ID, an eID list, a more-token object, and/or an error message if appropriate.

0453The following are exemplary expected interfaces of components of the query service.

0454The storage node locator <b>368</b> may expose an interface that may be used to discover a ranked list of storage hosts for write and list-attribute operations: <ul id="ul0052" list-style="none"><li id="ul0052-0001" num="0455"> GetStorageNodes (subscriber identifier, bucket identifier) </li></ul>

0456GetStorageNodes accepts a subscriber identifier and a bucket identifier, and returns a list of one or more storage nodes <b>370</b>.

0457The group health <b>226</b> component may expose one or more interfaces that may be used by the query node locator <b>354</b> to locate available query TSAR nodes <b>360</b>: <ul id="ul0053" list-style="none"><li id="ul0053-0001" num="0458"> Status (group) </li></ul>

0459Status returns status information for nodes in the specified group. If no status for the nodes in the group are known, then no status (or “status unknown”) is returned. In one embodiment, the status may be returned as a vector of qualities for each node: {status, [{Quality, Level}, {}. . . ]. Status information may include one or more of, but is not limited to, disk space, read “temperature”, liveness, etc. <ul id="ul0054" list-style="none"><li id="ul0054-0001" num="0460"> Monitor (group, callback) </li></ul>

0461Monitor returns group status changes through asynchronous callbacks.

0000Stress Management

0462Embodiments of the searchable data service may implement a distributed, non-centralized, automated stress management mechanism. In embodiments, each node in the searchable data service may manage its own resources as much as possible. The nodes may monitor their resource usage, and may communicate with a limited set of other nodes about their resource useage. When a resource usage is too high on a node and goes out of the comfort zone, the resource may be referred to as being hot. A resource that is not being used enough may be referred to as being cold. Each node may have actions that may be performed to keep its resource usage within a comfort zone.

0463In one embodiment, stress management may be modular, with separate processes controlling the monitoring, analysis/decisions, and actions to be performed In one embodiment, disk space may be actively managed by the automated stress management mechanism. Other embodiments may actively manage other system resources, including one or more of, but not limited to, communications bandwidth, read load, write load, and/or CPU usage or load, or combinations thereof.

0464Embodiments of the stress management mechanism may provide functionality including, but not limited to, the automated monitoring of critical resources, analysis of resource usage, and decisions on and performance of actions to keep resource usage in the comfort zone. Actions performed by the stress management mechanism may be performed so that they do not generate system loads that may impact overall system performance, availability, and/or reliability.

0465In embodiments, usage metrics for resources that may be monitored on a searchable data service node may include one or more of, but are not limited to: o Storage (e.g., disk) space: Some embodiments may monitor the percentage of available and/or used storage space on storage nodes for use in determining if the available storage space is in the comfort zone. <ul id="ul0055" list-style="none"><li id="ul0055-0001" num="0466"> CPU (processor) load: Some embodiments may monitor CPU (processor) usage. One embodiment may monitor queue depth and/or one or more other CPU usage metrics. The percentage of a node's potential throughput that is being used may be monitored for use in determining if the CPU usage is in the comfort zone. </li><li id="ul0055-0002" num="0467"> Read load: Some embodiments may monitor the number of disk reads. Reads may be driven primarily by queries and secondarily by “list attribute” calls. Embodiments may ensure that these calls are not silently lost and that, if a call cannot be performed, the call returns an error. </li><li id="ul0055-0003" num="0468"> Write load: Some embodiments may monitor the number of disk writes. When a host/disk has too much write load, update of eID attributes may slow down. Embodiments may ensure that the writes are not silently lost and that, if a call cannot be performed, the update returns an error. </li></ul>

0469In one embodiment, resource load logs may be kept on each node with moving window averages showing recent activity. When, for example, disk space is too hot for the comfort zone of a storage node, data may be moved from the storage node to one or more other storage nodes. In one embodiment, the stress management mechanism may increase disk space (or another resource) on a node before the resource reaches a critically low state.

0470In one embodiment, when a disk gets too full on a storage node (i.e., when the disk space resource usage on the storage node is too hot and is thus out of or approaching being out of the comfort zone for the storage node), data may be moved off the disk. In one embodiment, this may be performed with a minimum of data migration.

0471<figref idref="DRAWINGS">FIG. 15</figref> is a flowchart of a stress management method for a searchable data service system as described herein, according to one embodiment. A searchable data service system may be implemented on a plurality of nodes. The nodes may be located in one data center or may be dispersed across two or more data centers. The data centers may be geographically dispersed. In one embodiment, the searchable data service may include at least a coordination subsystem, a query subsystem and a storage subsystem. In one embodiment, the plurality of nodes may include one or more coordinator nodes that implement the coordination subsystem, one or more query nodes (also referred to as query TSAR nodes) that implement the query subsystem, and one or more storage nodes that implement the storage subsystem. In one embodiment, a Web services platform may provide a Web service interface to the searchable data service that provides one or more interface calls to client applications of the searchable data service.

0472In one embodiment, the plurality of nodes may self-organize into two or more node groups each including a subset of the plurality of nodes. In one embodiment, the node groups may include one or more storage node groups each including a subset of the storage nodes, one or more query node groups each including a subset of the query nodes, and one or more coordinator node groups each including a subset of the coordinator nodes. In one embodiment, each query node and each coordinator node may include an instance of a storage node locator component of the searchable data service configured to locate appropriate storage nodes to receive service requests, and the node groups may include one or more storage node locator groups each including a subset of the query nodes and the coordinator nodes. Other embodiments may include other types of node groups.

0473As indicated at <b>1200</b>, each node in a node group may monitor one or more usage metrics for each of one or more local resources of the node used in supporting searchable data service functionality on the node. In one embodiment, nodes in the node group may propagate usage metrics for local resources to other nodes in the node group in accordance with a gossip protocol. As indicated at <b>1202</b>, one of the nodes in the node group may detect that a monitored usage metric for one of the local resources of the node has crossed a boundary of a specified comfort zone for the usage metric. As indicated at <b>1204</b>, the node may communicate with at least one other node in the node group to transfer at least part of the resource usage for the local resource on the node to another node in the node group that includes a similar resource. In one embodiment, a gossip protocol and/or an anti-entropy protocol may be used in communicating with the at least one other node. Note that transferring at least part of the resource usage for the local resource to another node in the node group may move the monitored usage metric for the local resource on the node into the specified comfort zone for the usage metric on the node.

0474The following is an exemplary stress management algorithm for managing disk load that may be implemented by a stress management mechanism in a searchable data service system according to one embodiment. Note that the algorithm handles both adding new hosts to the searchable data service system when necessary and increasing disk space on individual hosts (storage nodes) when necessary. The individual hosts may use an implementation of relevant parts of this algorithm to locally manage disk space usage. Note that other embodiments may use other algorithms or modifications of this algorithm.

0000Definitions:

0000<ul id="ul0056" list-style="none"><li id="ul0056-0001" num="0475"> D_a=Average percent of disk usage across all storage nodes. </li><li id="ul0056-0002" num="0476"> D_th=Disk usage threshold. The high edge of the comfort zone. </li><li id="ul0056-0003" num="0477"> D_c=Low edge of the comfort zone. </li><li id="ul0056-0004" num="0478"> D_i=percent of disk usage on a host H_i. </li><li id="ul0056-0005" num="0479"> P_i=A partition on host H_i. <br /> Exemplary Algorithm: </li><li id="ul0056-0006" num="0480"> If D_a>D_th, add a host. </li><li id="ul0056-0007" num="0481"> If D_i>D_th, publish the list of partitions that H_iis offering to move. The list may include one or more, or even all, of H_i's partitions. <br /> Hosts where D_a<D_cmay bid for partitions from the list that they can accept without going over D_th. </li><li id="ul0056-0008" num="0482"> H_imay accept one or more bids such that: </li><li id="ul0056-0009" num="0483"> D_c<D_i(new)<D_th</li><li id="ul0056-0010" num="0484"> migration costs are low </li><li id="ul0056-0011" num="0485"> partitions go to disks with the most free space <br /> After a period, if H_i's receives no bids that will get it under D_th, split a partition (in one embodiment, the smallest partition) on H_iand re-offer an updated list of partitions. </li></ul>

0486In one embodiment, new partitions may be offered using the same or a similar mechanism. A default size may be used in place of the real (near zero) initial size for the new partitions.

0487In one embodiment, to save large free spaces on disks for larger partitions, the above algorithm may be modified so that partitions are more likely to be moved to a disk if that move may put the disk into the comfort zone. In this embodiment, hosts that are in the comfort zone may not bid on partitions. This modification may help to avoid moving smaller partitions onto disks that have a large amount of free space, thus saving that free space for larger partitions.

0488Other embodiments may implement one or more other rules for moving partitions that may be applied in the execution of the disk space stress management algorithm. For example, one embodiment may implement rules that may enable the packing of disks (decreasing D_thand/or the width of the comfort zone) with partitions that have had very little recent growth. As another example, one embodiment may implement rules that may enable the moving of partitions off of disks that have had significant recent growth and are nearing D_thduring periods of low activity.

0000Group Communication

0489The group communication <b>222</b> component may be used, for example, to enable other components of the searchable data service to maintain weakly-consistent replicated databases of indexing information. Group communication <b>222</b> may “carry” updates to one or more of, but not limited to, the following kinds of replicated data sets: <ul id="ul0057" list-style="none"><li id="ul0057-0001" num="0490"> Searchable data service entities in the standalone storage/indexing/querying subsystem(s). </li><li id="ul0057-0002" num="0491"> Bucket partitioning information and standalone storage host replication group directories. </li><li id="ul0057-0003" num="0492"> Group membership information for query subsystem hosts and request router <b>202</b> hosts. </li></ul>

0493Weakly-consistent means that reads of replicated data may not reflect changes made by the most recent writes that were applied elsewhere in the replication group. In the absence of further changes, all replicas should converge to the same values, though that convergence may be delayed, for example by network partitions and/or node reboots.

0494In one embodiment, group communication may rely on two methods: gossip and anti-entropy. Gossip (or “rumor mongering”) is an unreliable multicast through probabilistic flooding. Anti-entropy is a process of selecting a random peer host and looking for and resolving any differences between the peer databases on the selected host and the peer databases on other host(s). In one embodiment, a high-level and a low-level anti-entropy may be performed.

0495High-level anti-entropy may compare a peer's logs of gossiped updates to handle cases where the probabilistic flooding of messages may have missed a host. High-level anti-entropy may be performed without reference to the underlying database. Low-level anti-entropy compares the databases (alternatively, in one embodiment, aggregate statistics of the databases, such as checksuins), and may handle cases where a node has rebooted or otherwise lost its message log, or where a node is joining a replication group and uses low-level anti-entropy to idempotently get a copy of the database.

0496In one embodiment, the group communication <b>222</b> component may have no knowledge of the implementation of the underlying database. The group communication <b>222</b> component provides the database with a call to propagate an update, and relies on the database to provide callbacks for processing received updates and for performing low-level anti-entropy.

0497The group communication <b>222</b> component may have frequent interaction with the group health <b>226</b> component. In one embodiment, the two components may be implemented in separate processes. In another embodiment, both of these components may be implemented within the same process so that the two components may share data structures.

0000Replication Group Life Cycle

0498<figref idref="DRAWINGS">FIG. 16</figref> illustrates the life cycle of a replication group <b>300</b> in a searchable data service according to one embodiment. New hosts <b>310</b> may be added to replication group <b>300</b>, and existing hosts <b>310</b> may be removed from or leave replication group <b>300</b>. New hosts <b>310</b> (e.g., host <b>310</b>J) may be added to replication group <b>300</b> by declaring or plegding <b>320</b> themselves as pledges <b>304</b>. Pledged hosts <b>310</b> (e.g., host <b>310</b>G and <b>310</b>H) may receive gossipped updates to the replicated data set. The pledged hosts <b>310</b> may then select an existing replication group <b>300</b> member (e.g., host <b>310</b>F) and perform low-level anti-entropy. Since pledged hosts <b>310</b> may also receive all updates, when the anti-entropy finishes, the pledged hosts <b>310</b> may be as up-to-date as any other replication group <b>300</b> member, and may thus initiate themselves into replication group <b>300</b>.

0499A host <b>310</b> (e.g., host <b>310</b>K) may leave replication group <b>300</b>, for example through failure or resignation. Resignation may require synchronization, as too many simultaneous resignations may cause the replication group <b>300</b> to fall below its minimal membership requirements.

0500In one embodiment, group membership changes may be sent to one or more other groups of hosts, known as next-of-kin groups <b>302</b>. For a replication group, a next-of-kin group is a storage node locators group. For a storage node locators group, the next-of-kin groups are all replication groups. A replication group is a group of storage nodes that store replicas of a particular partition. Note that replication groups are illustrated in <figref idref="DRAWINGS">FIG. 9C</figref> and <figref idref="DRAWINGS">FIG. 10</figref> as replication groups <b>256</b>. The storage node locators group is a group of nodes (hosts) in the searchable data service that each include an instance of storage node locator <b>216</b>.

0501Embodiments of a searchable data service may include one or more of, but are not limited to, the following types of groups of hosts, or nodes. Note that a name is provided for each type of group. These names are exemplary, and are not intended to be limiting: <ul id="ul0058" list-style="none"><li id="ul0058-0001" num="0502"> snl_hosts: includes some or all nodes implementing a storage node locator (snl); in one embodiment, all coordination and query aggregation subsystem nodes. </li><li id="ul0058-0002" num="0503"> qtsar-hosts: includes some or all nodes in the query subsystem. This may also be referred to as a query node group. </li><li id="ul0058-0003" num="0504"> coord_datacenter_hosts: all coordinator nodes in the given data center. This may also be referred to as a coordinator node group. </li><li id="ul0058-0004" num="0505"> sn_subscriber_bucket_mask_value_hosts: the replication group for the named partition. “sn” represents “storage node”. This is what is referred to elsewhere as a partitions group, but may also be referred to as a storage node group. <br /> Group Communication Interfaces </li></ul>

0506The following describes exemplary interfaces (e.g., calls and callbacks, both eternal and internal (peer-to-peer)) that may be exposed or expected by a group communication <b>222</b> component of a searchable data service according to one embodiment. Note that these interfaces are exemplary, and are not intended to be limiting. Other embodiments may include other interfaces, or may not include one or more of these interfaces.

0000Calls

0000<ul id="ul0059" list-style="none"><li id="ul0059-0001" num="0507"> constructor(argument(s)) </li></ul>

0508One embodiment may provide a constructor call to construct a new replication group <b>300</b>. This constructor may accept one or more parameters as arguments including, but not limited to, a minimum number of group members required to successfully acknowledge and service initial updates received via a gcast call (see below). <ul id="ul0060" list-style="none"><li id="ul0060-0001" num="0509"> gcast(Group, Msg) </li></ul>

0510gcast initiates a gossiped message within a group. Group is a string naming the group. Msg is a value specifying the message to be sent to the group. This may be given as the msg argument to the apply callback for other group members.

0511In one embodiment, the results of a gcast call is an object containing one or more of, but not limited to, the following elements: <ul id="ul0061" list-style="none"><li id="ul0061-0001" num="0512"> Hosts: An array of strings listing the storage nodes which have acknowledged the update so far. </li><li id="ul0061-0002" num="0513"> Durable: A boolean indicating whether the message was initially propagated to the minimum number of group members. The system may continue to attempt to communicate the message, even if false is returned. </li><li id="ul0061-0003" num="0514"> Cookie: A value that may be later given to gsync to see if the message has been acknowledged by all group members. </li></ul>

0515In one embodiment, a gcast call may generate one or more of, but not limited to, the following errors: <ul id="ul0062" list-style="none"><li id="ul0062-0001" num="0516"> invalid group type </li><li id="ul0062-0002" num="0517"> invalid group name </li><li id="ul0062-0003" num="0518"> gsync(Cookie) </li></ul>

0519gsync returns a boolean indicating whether a gossipped message has reached all non-failed group memebers. Cookie is a value that was returned by a successful gcast call. The results of a gsync call may be a boolean indicating whether all group members have acknowledged the message. In one embodiment, a gsync call may generate, but is not limited to, an invalid cookie error.

0000Callbacks

0000<ul id="ul0063" list-style="none"><li id="ul0063-0001" num="0520"> apply(Group, Msg) </li></ul>

0521The apply callback applies the change described by the given message to a replicated data set. Group is a string indicating the group name. Msg is a value indicating the message to be applied.

0522In one embodiment, the results of a gcast call may include one or more of, but are not limited to, one of the following: <ul id="ul0064" list-style="none"><li id="ul0064-0001" num="0523"> OK: the change was successfully applied, though perhaps not in whole due to more recently-ordered changes. </li><li id="ul0064-0002" num="0524"> DUP: or “duplicate”. The specified change has previously been received. </li><li id="ul0064-0003" num="0525"> LATE: The specified change has been obsolete by more recently-ordered changes; </li><li id="ul0064-0004" num="0526"> Error: A string giving an error reason. The change cannot be applied due to the reason specified by the Error. As a result, in one embodiment, a low-level anti-entropy session may be requested with a peer to perform self-repair (see below). </li><li id="ul0064-0005" num="0527"> antientropy(Group, Host) </li></ul>

0528The antientropy callback initiates an anti-entropy session with the specified peer Host for the data associated with the named group. Group is a string indicating the name of the group. Host is a string indicating the name of the peer Host with which to perform anti-entropy antientropy may return a boolean indicating whether the entire data set was traversed. If false, another anti-entropy session for the same group may be initiated, preferably with a different peer host. In one embodiment, an antientropy callback may generate, but is not limited to, a group invalid or a host invalid error.

0000Peer-to-Peer Calls

0529Peer-to-peer calls may be internal to an implementation of the searchable data service. These calls are made between or to members of specified groups. <ul id="ul0065" list-style="none"><li id="ul0065-0001" num="0530"> rumor(Group, Originator, Seqno, OrigVtime, Msg) </li></ul>

0531The rumor peer-to-peer call spreads an update in a group by rumor-mongering. Group is a string indicating the name of the group in which the update is to be spread. Originator is a string indicating the name of the originating host. Seqno indicates the originator's sequence number for the update. OrigVtime indicates the originator's virtual time for the update. Msg indicates the update that is being spread, which is to be applied to the remote database through the apply callback. The results of a rumor call may be a boolean indicating whether the rumor has been successfully received. In one embodiment, a rumor call may generate, but is not limited to, a group invalid error. <ul id="ul0066" list-style="none"><li id="ul0066-0001" num="0532"> request_membership(Group, Mode, Generation, Seqno) </li></ul>

0533The request_membership peer-to-peer call requests a voluntary membership change to be made for the sender in the receiver's group membership view. Group is a string indicating the name of the group. Mode indicates the type of membership change; in one embodiment, this may be one of “pledge”, “initiate”, and “resign”. Generation indicates the sender's generation number, which may be guaranteed to increment after reboots. Seqno indicates the originator's sequence number for the operation, so that an acknowledgement vector (see below) may be used to indicate when all group members have seen the operation. The results of a request_membership call may be a boolean indicating whether the recipient has made the requested group membership change. In one embodiment, a request_membership call may generate, but is not limited to, a group invalid error.

0534In one embodiment, a received request_membership call may be forwarded to one or more other group members by the receiver. In one embodiment, the receiver may return a list of other group members to which the request_membership call has been forwarded to the sender. <ul id="ul0067" list-style="none"><li id="ul0067-0001" num="0535"> failure(Group, Host, Generation) </li></ul>

0536The failure peer-to-peer call announces that a group member has been identified as having failed. Group is a string indicating the name of the group. Host identifies the failed host. Generation: indicates the generation of the failed host at the time of failure. <ul id="ul0068" list-style="none"><li id="ul0068-0001" num="0537"> fast_anti_entropy(Group, View, SummaryVec, AcknowledgementVec) </li></ul>

0538The fast_anti_entropy peer-to-peer call initiates a fast or high-level phase of anti-entropy to exchange updates possibly missed by rumor-mongering. An exchange of these operations may be followed by any necessary rumor operations to bring the two hosts into sync. Group is a string indicating the name of the group. View is an object representing the group membership view. SummaryVec is an object representing the summary vector. AcknowledgementVec is an object representing the acknowledgement vector. The results of a fast_anti_entropy call may be a boolean indicating successful processing of the information, to be followed by a reciprocal call and an excange of rumor operations until the two hosts have exchanged all available messages. In one embodiment, a fast anti entropy call may generate, but is not limited to, a group invalid error.

0539In one embodiment, a receivedfast_anti_entropy call may be forwarded to one or more other group members by the receiver. In one embodiment, the receiver may return a list of other group members to which thefast_anti_entropy call has been forwarded to the sender.

0000Group Membership and Health

0540In one embodiment, a group health <b>226</b> component may allow one or more other components of the searchable data service to identify sets of nodes that the components may monitor. The group health <b>226</b> component may then be queried by the other components for automatically-refreshed health information about those nodes. In one embodiment, the group health <b>226</b> component may also perform as a failure detection mechanism.

0541In embodiments of the searchable data service, hosts (nodes) may exchange health information about themselves and other nodes via the group health <b>226</b> component and the group communication <b>222</b> component. In one embodiment, if a searchable data service node is not communicating with other nodes, whether due to a node failure, a network failure, or some other reason, the staleness of the node's information may be noticed by the other nodes, and a timer may be used to eventually declare the silent node as failed. This encapsulation of time may help to simplify other components by allowing the components to work asynchronously—if a node A is waiting for a response from a node B, node A may eventually either receive a response from node B or be notified of node B's failure. In one embodiment, another node may be determined to have failed or gone offline if a group health message is not received from that node (either directly or through gossip) for a period equal to or greater than a prespecified timeout period after the last received group health message.

0542In one embodiment, distributed load averaging may be controlled at least in part through the group membership and health <b>226</b> component. For example, in one embodiment, group health <b>226</b> component may provide a mechanism to select a best member node from a replication group, taking current load averages and distances into account.

0543In one embodiment, there may be an instance of group health <b>226</b> component on each node in the searchable data service. In one embodiment, to allow other nodes to detect a node's failure, the group health <b>226</b> component on each node may periodically send a group health message, also referred to as a heartbeat message, to one or more neighbor nodes. The heartbeat message may include current local health statistics for the node. These statistics may include statistics on one or more of, but not limited to, the following node health information metrics: <ul id="ul0069" list-style="none"><li id="ul0069-0001" num="0544"> Processor usage metrics—e.g., CPU (processor) load average/run queue depth, etc. </li><li id="ul0069-0002" num="0545"> Storage and/or memory resource usage metrics—e.g., disk I/O, disk free space, paging/swapping metrics, etc. </li><li id="ul0069-0003" num="0546"> Network/bandwidth resource usage metrics—e.g., network traffic metrics for a network communications resource. </li></ul>

0547The statistics may be averages over a time period (or over different time periods for different ones of the metrics), for example over one minute, or five minutes. In one embodiment, the averages for the node health information metrics may be correlated against operation counts in order to establish an estimate of a marginal change in load with an increase or decrease in operations. In one embodiment, the group health <b>226</b> component may query one or more other local components as necessary to get a per-bucket breakdown of operations in the last time period for averaging. The statistics may be augmented with a prediction of change in CPU load (or bandwidth, or storage, etc.) that may be realized in response to a change in the number of operations, e.g. “what will the disk I/O stress be like if an additional <b>150</b> queries per second are taken on?” This, for example, may allow a partition manager <b>232</b> component on a storage node to estimate what the loads may be like if one or more proposed changes to the configuration are made.

0548In one embodiment, a heartbeat message may be propagated to components on nodes throughout the searchable data service system or within a group of nodes in the searchable data service system via an epidemic, or gossip, protocol. In one embodiment, the communications may be performed via a group communications <b>222</b> component of the searchable data service, as described above. In one embodiment, group health information may be piggybacked on other searchable data service inter-node and inter-component messages.

0549If a node has not received a heartbeat message for another node for a period in excess of a specified threshold or time period (e.g., five minutes), the node may assume that the other node has failed. If a node does not receive any heartbeats from any other nodes for a period, the node may assume that its network connection has failed.

0550In one embodiment, when a node receives a heartbeat message, the node may check an internal table to see if this is the most recent heartbeat message that the node has seen from the originator node. If it is not, the heartbeat message is discarded. If it is the most recent heartbeat message from the originator node, the internal table is updated, and the heartbeat message may then be sent to one or more other neighbor nodes. In one embodiment, the neighbor nodes may be randomly selected. In one embodiment, the neighbor nodes may be chosen with a bias toward nearer neighbor nodes, in order to reduce the number of times the heartbeat is sent over WAN links. However, the probability of successfully sending a heartbeat message to distant nodes over a network (and of the distant nodes receiving the heartbeat message) should be high enough to realize a desired level of confidence that the heartbeat will eventually reach every other data center in the searchable data service system.

0551In one embodiment, the neighbor nodes to which a heartbeat message is forwarded may be selected on a per-monitored-group basis. For example, if node A's group health <b>226</b> component is monitoring groups G<b>1</b>, G<b>2</b>, and G<b>3</b>, each of which node A is a member, and is also monitoring groups G<b>4</b>, G<b>5</b>, and G<b>6</b>, of which node A is not a member, then node A's heartbeat messages may be sent to N hosts in each of the six groups. One embodiment may optimize selection of nodes to which heartbeat messages are forwarded for groups that have overlapping memberships. For example, if a node B in group G<b>2</b> is selected to receive a heartbeat message from node A, and node B is also a member of groups G<b>4</b> and G<b>6</b>, then node B may also be selected to receive the heartbeat message for those other groups as well.

0552If a node has not seen a health update from a monitored node for a period, e.g. 5 minutes, the node may perform a health anti-entropy with a different node, which in one embodiment may be selected according to a probability that decreases with distance from the node. Other embodiments may use other methods or metrics or combinations thereof to select a different node with which a health anti-entropy may be performed. For example, in one embodiment, the different node may be selected according to a probability that decreases with effective network and node utilization costs. If the anti-entropy does not yield an update for the monitored node, the monitored node may be identified as dead or unavailable to local components on the monitoring node.

0553In one embodiment, one or more gossip, or epidemic, protocols may be used for weakly-consistent multicasting of updates to health information. In one embodiment, the group health <b>226</b> component may not be considered a regular client of the group communication <b>222</b> component, since the group communication <b>222</b> component relies on group membership and health <b>226</b> component.

0554The group health <b>226</b> component may have frequent interaction with the group communication <b>222</b> component. In one embodiment, the two components may be implemented in separate processes. In another embodiment, both of these components may be implemented within the same process so that the two components may share data structures.

0555The amount of network traffic required for performing health updates may be a limiting factor for scaling a searchable data service, due to potentially large groups of nodes. Therefore, in one embodiment, the groups of nodes in a searchable data service may be organized as a hierarchy of groups, thus allowing large data sets to be addressed while limiting the size of any single group of nodes.

0556<figref idref="DRAWINGS">FIG. 17</figref> illustrates a method for monitoring group health in a searchable data service system according to one embodiment. A searchable data service system may be implemented on a plurality of nodes. The nodes may be located in one data center or may be dispersed across two or more data centers.

0557The data centers may be geographically dispersed. In one embodiment, the searchable data service may include at least a coordination subsystem, a query subsystem and a storage subsystem. In one embodiment, the plurality of nodes may include one or more coordinator nodes that implement the coordination subsystem, one or more query nodes (also referred to as query TSAR nodes) that implement the query subsystem, and one or more storage nodes that implement the storage subsystem. In one embodiment, a Web services platform may provide a Web service interface to the searchable data service that provides one or more interface calls to client applications of the searchable data service.

0558In one embodiment, the plurality of nodes may self-organize into two or more node groups each including a subset of the plurality of nodes. In one embodiment, the node groups may include one or more storage node groups each including a subset of the storage nodes, one or more query node groups each including a subset of the query nodes, and one or more coordinator node groups each including a subset of the coordinator nodes. In one embodiment, each query node and each coordinator node may include an instance of a storage node locator component of the searchable data service configured to locate appropriate storage nodes to receive service requests, and the node groups may include one or more storage node locator groups each including a subset of the query nodes and the coordinator nodes. Other embodiments may include other types of node groups.

0559As indicated at <b>1300</b>, each node in a node group may collect local health information for the node. As indicated at <b>1302</b>, each node in the node group may periodically or aperiodically send a message including collected local health information for the node to at least one other node in the node group. As indicated at <b>1304</b>, each node in the node group may periodically or aperiodically receive messages originating from one or more other nodes in the node group and including collected local health information for the other nodes. In one embodiment, the local health information for a node may include one or more of, but is not limited to: one or more storage resource usage metrics for a local storage resource; one or more processor usage metrics for a local processor resource; and one or more network usage metrics for a network communications resource.

0560In one embodiment, the nodes in the node group may be configured to propagate the messages within the node group in accordance with a gossip protocol. In one embodiment, the nodes in the node group may piggyback the health information on other searchable data service messages to other nodes in the node group.

0561In one embodiment, the health messages may be used as heartbeat messages to detect if another node in the node group has gone offline. In this embodiment, as indicated at <b>1306</b>, one of the nodes in the node group may determine that another node in the node group has gone offline if a new message including collected local health information for the other node is not received within a specified period.

0562In one embodiment, upon detecting that a new message including collected local health information for another other node has not been received from a particular node in the node group for a specified period, the node may perform an anti-entropy operation with one or more other nodes in the node group to obtain updated health information for the nodes in the node group. If the anti-entropy operation does not produce updated health information for the particular node, the node may then determine that the particular node has gone offline.

0563In one embodiment, a node in the node group may compare collected local health information for the node to local health information for at least one of the other nodes in the node group received in messages from the other nodes. The node may use the comparison in making local node health decisions for the node.

0000Group Membership and Health Interfaces

0564The following describes exemplary interfaces (e.g., calls and callbacks, both eternal and internal (peer-to-peer)) that may be exposed or expected by a group health <b>226</b> component of a searchable data service according to one embodiment. Note that these interfaces are exemplary, and are not intended to be limiting. Other embodiments may include other interfaces, or may not include one or more of these interfaces.

0000Calls

0000<ul id="ul0070" list-style="none"><li id="ul0070-0001" num="0565"> add(Group, Host) </li></ul>

0566The add call adds a specified host (node) to a specified group. This call may result in the creation of the group if not already present. <ul id="ul0071" list-style="none"><li id="ul0071-0001" num="0567"> del(Group, Host) </li></ul>

0568The del call deletes a specified host (node) from a specified group. This call may result in the deletion of the specified group itself if the deleted host was the only host in the group. <ul id="ul0072" list-style="none"><li id="ul0072-0001" num="0569"> gdel(Group) </li></ul>

0570The gdel call deletes the specified group. <ul id="ul0073" list-style="none"><li id="ul0073-0001" num="0571"> status(Group) </li></ul>

0572The status call returns status information for all nodes in the specified group. The status results may be returned in an object that includes the node names in the group, and status information on each of the named nodes. The status information may include, for each node, an indication as to whether the node is known; that is, if the node is known to the requestor via previous information received about the named node. If the node is not known, other status information about that particular node may not be valid. If the node is known, then the status information for the node may include an indication if the node is currently alive, and may also include other information about the node. <ul id="ul0074" list-style="none"><li id="ul0074-0001" num="0573"> monitor(Group) </li></ul>

0574The monitor call returns group status changes for the specified group through one or more asynchronous callbacks. <ul id="ul0075" list-style="none"><li id="ul0075-0001" num="0575"> unmonitor(Group) </li></ul>

0576The umonitor call turns off asynchronous callbacks for the specified group. This call may undo a monitor call for the specified group.

0000Callbacks

0000<ul id="ul0076" list-style="none"><li id="ul0076-0001" num="0577"> update(Group, Host, Status) </li></ul>

0578The update callback provides immediate notification of a status change for the specified host (node) in the specified monitored group.

0000Peer-to-Peer Calls

0000<ul id="ul0077" list-style="none"><li id="ul0077-0001" num="0579"> heartbeat(Originator, OrigVtime, StatVec) </li></ul>

0580The heartbeat peer-to-peer call propagates a rumor of a heartbeat. Originator indicates the host originationg the heartbeat. OrigVtime indicates the virtual time of the heartbeat. StatVec is an object that includes statistics on one or more named metrics and arrays of values for the statistics, where the first element is the normalized stress and the second element is the estimated per-operation change in the stress. Exemplary metrics on which statistics may be included may include one or more of, but are not limited to: <ul id="ul0078" list-style="none"><li id="ul0078-0001" num="0581"> cpu: CPU load average or run queue depth for a period (e.g., for one minute). </li><li id="ul0078-0002" num="0582"> diskspace: disk space utilization percentage and usage (e.g., in gigabytes). </li><li id="ul0078-0003" num="0583"> diskio: disk I/O operations. </li><li id="ul0078-0004" num="0584"> net: network I/O operations. </li><li id="ul0078-0005" num="0585"> mempage: memory paging. <br /> Administrative Console </li></ul>

0586One embodiment of the searchable data service may provide an administrative console that may allow an administrator to monitor the behavior of the searchable data service system. <figref idref="DRAWINGS">FIG. 18</figref> illustrates a high-level architecture of an administrative console in a searchable data service system according to one embodiment. The administrative console <b>400</b> may collect information from hosts <b>410</b> in the searchable data service system. In a searchable data service system implementation, a single event (a query or add, for example) may result in many hosts in the system communicating with each other. Providing an administrative console <b>400</b> that can monitor, capture, analyze, summarize and display information on events and the resulting cascade of activity (e.g., messages) in the system that may follow an event may be valuable in system monitoring, optimization, and troubleshooting during various phases of a searchable data service system.

0587An administrative console <b>400</b> may be used during the development phase of a searchable data service system to, for example, understand system behavior, debug, and detect areas that may need optimization. During the production phase, an administrative console <b>400</b> may be used, for example, to monitor the health of the system, identify problems, and to predict and address issues before they become critical.

0588In an embodiment illustrated in <figref idref="DRAWINGS">FIG. 18</figref>, administration of a searchable data service may be implemented in a distributed architecture, with components of the distributed administrative system residing on two or more hosts. A remote administration <b>402</b> application may reside on a host system (the administrative console <b>400</b>). One or more of hosts <b>410</b> in the searchable data service system may each include a local administration <b>412</b> module that monitors and collects information on the searchable data service activities, health information, and communications of the searchable data service components <b>414</b> in that host <b>410</b>, including component-to-component communications between components <b>414</b> on that host and between components <b>414</b> on different hosts <b>410</b>.

0589In one embodiment, remote administration <b>402</b> application may establish communications channels (e.g., RPC (Remote Procedure Call) or HTTP communications channels) with the local administration <b>412</b> modules at specified searchable data service nodes (hosts <b>410</b>), and requests to monitor one or more searchable data service components <b>414</b>. Each local administration <b>412</b> module may then establish a connection with the requested searchable data service components <b>414</b>, and requests that those searchable data service components <b>414</b> start sending messages for monitoring to the local administration <b>412</b> module. The local administration <b>412</b> modules forward these messages to the remote administration <b>402</b> application.

0590In one embodiment, remote administration <b>402</b> application may provide an interactive client interface to the human client, for example an administrator. The client may, via the client interface, direct the remote administration <b>402</b> application to connect to particular (or all) local administration <b>412</b> modules, and may direct the local administration <b>412</b> modules, via the remote administration <b>402</b> application, to enable/disable the monitoring of particular searchable data service components <b>414</b>.

0591Administrative console <b>400</b> may capture, log/store, perform analysis of, and graphically and/or textually display the collected information and/or summaries of the collected information for a client (e.g., a system administrator). In one embodiment, the administrative console <b>400</b> may enable or perform one or more of, but is not limited to, the following activities (referring to the components illustrated in <figref idref="DRAWINGS">FIG. 6</figref>):

0592Capture, log and display messages between searchable data service hosts. These messages may include, but are not limited to: messages between request routers <b>202</b>, messages between storage node locators <b>216</b>, messages between query node locators <b>220</b>, messages between eID update manager s <b>230</b>, messages between request routers <b>202</b> and query TSARs <b>212</b>, messages between request routers <b>202</b> and eID update manager s <b>230</b>, messages between query TSARs <b>212</b> and query processors <b>228</b>, messages between partition managers <b>232</b> and storage node locators <b>216</b>, and messages between partition managers <b>232</b>. <ul id="ul0079" list-style="none"><li id="ul0079-0001" num="0593"> Capture, log and display messages (e.g., RPC messages) between modules or components within a searchable data service host. These messages may include, but are not limited to: request router <b>202</b>-query node locator <b>220</b> messages, request router <b>202</b>-storage node locator <b>216</b> messages, partition manager <b>232</b>-eID update manager <b>230</b> messages, query TSAR <b>212</b>-storage node locator <b>216</b> messages, storage node locator <b>216</b>-group membership and health <b>226</b> messages, query node locator <b>220</b>-group membership and health <b>226</b> messages, partition manager <b>232</b>-group membership and health <b>226</b> messages, storage node locator <b>216</b>-group communication <b>222</b> messages, and query node locator <b>220</b>-group communication <b>222</b> messages. </li><li id="ul0079-0002" num="0594"> Capture and display content of eID Stores <b>236</b> and query index stores <b>234</b>. </li><li id="ul0079-0003" num="0595"> Monitor and display group membership information (e.g., snl_hosts, qtsar_hosts, etc.) </li><li id="ul0079-0004" num="0596"> View the states of storage node locators <b>216</b>: mappings between hosts and partition replicas. </li><li id="ul0079-0005" num="0597"> View the states of query node locators <b>220</b>: consistent hashing ring of query TSARs. </li><li id="ul0079-0006" num="0598"> Display contents of a query TSAR's query cache <b>214</b>. </li><li id="ul0079-0007" num="0599"> View the states of request router(s) <b>202</b>. </li><li id="ul0079-0008" num="0600"> View the states of partition managers <b>232</b>. </li><li id="ul0079-0009" num="0601"> Modify group membership lists. </li><li id="ul0079-0010" num="0602"> Initiate anti-entropy between two nodes. </li><li id="ul0079-0011" num="0603"> Add or remove resources from the system. </li><li id="ul0079-0012" num="0604"> Temporarily or permanently stop processing of one or more nodes </li></ul>

0605Referring again to <figref idref="DRAWINGS">FIG. 18</figref>, in one embodiment, the remote administration <b>402</b> application may provide one or more of, but is not limited to, the following interfaces. Note that these interfaces are exemplary and are not intended to be limiting: <ul id="ul0080" list-style="none"><li id="ul0080-0001" num="0606"> readMsg(String msg) </li></ul>

0607read Msg receives messages from local administration <b>412</b> modules. <ul id="ul0081" list-style="none"><li id="ul0081-0001" num="0608"> startMon(String host, int port) </li></ul>

0609startMon connects to a local administration <b>412</b> module at the specified host:port and enables all components <b>414</b> that are to be monitored for this local administration <b>412</b> module. <ul id="ul0082" list-style="none"><li id="ul0082-0001" num="0610"> stopMon(String host, int port) </li></ul>

0611stopMon stops the monitoring of all components <b>414</b> and disconnects from the local administration <b>412</b> module at the specified host:port. <ul id="ul0083" list-style="none"><li id="ul0083-0001" num="0612"> stopAllMon() </li></ul>

0613stopAllMon stops the monitoring of all components <b>414</b> and disconnects from all currently connected local administration <b>412</b> modules. <tables id="TABLE-US-00019" num="19"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="203PT" align="left" /><thead><row><entry /><entry /></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry /><entry>enableComp(String componentName)</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="28PT" align="left" /><colspec colname="1" colwidth="189PT" align="left" /><tbody valign="top"><row><entry /><entry>enableComp begins monitoring all connected hosts' components</entry></row><row><entry /><entry>414 identified by</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="217PT" align="left" /><tbody valign="top"><row><entry>componentName.</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="203PT" align="left" /><tbody valign="top"><row><entry /><entry>enableAllComp( )</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="28PT" align="left" /><colspec colname="1" colwidth="189PT" align="left" /><tbody valign="top"><row><entry /><entry>enableAllComp enables monitoring on all components 414 found</entry></row><row><entry /><entry>in a static input file.</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="203PT" align="left" /><tbody valign="top"><row><entry /><entry>disableComp(String componentName)</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="28PT" align="left" /><colspec colname="1" colwidth="189PT" align="left" /><tbody valign="top"><row><entry /><entry>disableComp stops monitoring all connected hosts' components</entry></row><row><entry /><entry>414 identified by</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="217PT" align="left" /><tbody valign="top"><row><entry>componentName.</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="203PT" align="left" /><tbody valign="top"><row><entry /><entry>disableAllComp( )</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="28PT" align="left" /><colspec colname="1" colwidth="189PT" align="left" /><tbody valign="top"><row><entry /><entry>disableAllComp stops monitoring all components 414, but does</entry></row><row><entry /><entry>not disconnect from</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="217PT" align="left" /><tbody valign="top"><row><entry>currently connected local administration 412 modules.</entry></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0614disableAliComp stops monitoring all components <b>414</b>, but does not disconnect from currently connected local administration <b>412</b> modules.

0000Local Administration Module

0615A local administration <b>412</b> module on a searchable data service host <b>410</b> serves as an intermediary between the remote administration <b>402</b> application and the local components <b>414</b>. Local administration <b>412</b> module waits for a remote administration <b>402</b> connection and, once connected to remote administration <b>402</b> application, handles enable/disable component <b>414</b> requests from that remote administration <b>402</b> application. Local administration <b>412</b> module may also forward information on searchable data service messages among local components <b>414</b> to the remote administration <b>402</b> application.

0616The following is an exemplary message format of searchable data service monitoring messages to the remote administration <b>402</b> application from local administration <b>412</b> modules, and is not intended to be limiting: <tables id="TABLE-US-00020" num="20"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="1"><colspec colname="1" colwidth="217PT" align="left" /><thead><row><entry /></row><row><entry namest="1" nameend="1" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry><host/hostname/nodeID>: <Component> <sent/received> on <to/from</entry></row><row><entry>who> <timestamp>:</entry></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="2"><colspec colname="OFFSET" colwidth="14PT" align="left" /><colspec colname="1" colwidth="203PT" align="left" /><tbody valign="top"><row><entry /><entry><msg></entry></row><row><entry /><entry namest="OFFSET" nameend="1" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0617In one embodiment, a local administration <b>412</b> module may provide one or more of, but is not limited to, the following interfaces. Note that these interfaces are exemplary and are not intended to be limiting: <ul id="ul0084" list-style="none"><li id="ul0084-0001" num="0618"> monMsg(String msg) </li></ul>

0619monMsg is called by a component <b>414</b> when the component <b>414</b> sends/receives a message. <ul id="ul0085" list-style="none"><li id="ul0085-0001" num="0620"> monBegin(String componentName) </li></ul>

0621monBegin looks up the port of the named component <b>414</b> in a static file, connects to local host:port, and calls monEnable() for the component <b>414</b>. <ul id="ul0086" list-style="none"><li id="ul0086-0001" num="0622"> monBeginAll() </li></ul>

0623monBeginAll reads a static input file that includes a list of components <b>414</b> and the components' ports, connects to the components <b>414</b> listed in the file, and calls monEnable() for each of the components <b>414</b>. <ul id="ul0087" list-style="none"><li id="ul0087-0001" num="0624"> monStop(String componentName) </li></ul>

0625monStop stops monitoring the named component <b>414</b>. <ul id="ul0088" list-style="none"><li id="ul0088-0001" num="0626"> monStopAll() </li></ul>

0627monStopAll stops all current component <b>414</b> monitoring activities.

0000Local Components

0628A local component <b>414</b> waits for a local administration <b>412</b> connection. Once connected to the local administration <b>412</b> module, a local component <b>414</b> may start sending messages for monitoring to the local administration <b>412</b> module when it receives an enable request from the local administration <b>412</b> module (which, in turn, occurs when the local administration <b>412</b> module receives an enable request from the remote administration <b>402</b> application). The local component <b>414</b> may stop sending messages for monitoring when it receives a disable request from the local administration <b>412</b> module.

0629The following is an exemplary message format of searchable data service monitoring messages to a local administration <b>412</b> module from local components <b>414</b>, and is not intended to be limiting: <ul id="ul0089" list-style="none"><li id="ul0089-0001" num="0630"> Component><sent/received> on <to/from who><timestamp>: <msg></li></ul>

0631In one embodiment, a local component <b>414</b> may provide one or more of, but is not limited to, the following interfaces. Note that these interfaces are exemplary and are not intended to be limiting: <ul id="ul0090" list-style="none"><li id="ul0090-0001" num="0632"> monEnable() </li></ul>

0633monEnable begins sending any sent/received messages to the local administration <b>412</b> module by invoking sendMsgToMon. <ul id="ul0091" list-style="none"><li id="ul0091-0001" num="0634"> monDisable() </li></ul>

0635monDisable stops sending messages to the local administration <b>412</b> module. <ul id="ul0092" list-style="none"><li id="ul0092-0001" num="0636"> sendMsgToMon(String msg) </li></ul>

0637When monitoring is enabled, sendMsgToMon sends any sent/received messages to the local administration <b>412</b> module by invoking monMsg(String msg).

0000Searchable Data Service System—Physical Implementation

0638<figref idref="DRAWINGS">FIG. 19</figref> illustrates an implementation of a searchable data service <b>720</b> in a networked environment according to one embodiment. Network <b>700</b> may represent, for example, the World Wide Web, or Internet. Alternatively, network <b>700</b> may represent a Local Area Network (LAN), or Wide Area Network (WAN). Searchable data service <b>720</b> may be implemented across one or more data centers <b>710</b> (e.g., data centers <b>710</b>A and <b>710</b>B). A data center <b>710</b> represents a local collection of computing devices, which may include, but are not limited to, server systems and storage devices. Data centers <b>710</b> may be geographically dispersed. Note that not all computing devices in a data center <b>710</b> may participate in searchable data service <b>720</b>.

0639Searchable data service hosts <b>722</b>A and <b>722</b>B, in data centers <b>710</b>A and <b>710</b>B respectively, represent individual computer systems (e.g., server systems) that host instances of searchable data service nodes, such as coordinator nodes <b>340</b>, query TSAR nodes <b>350</b>, and storage nodes <b>360</b> as illustrated in <figref idref="DRAWINGS">FIG. 4</figref>. In one embodiment, each searchable data service host <b>722</b> may host one and only one searchable data service node. In this embodiment, each searchable data service host <b>722</b> represents a distinct searchable data service node; each coordinator node <b>340</b>, query TSAR node <b>350</b>, and storage node <b>360</b> is instantiated on a separate computer system.

0640In another embodiment, a searchable data service host <b>722</b> may host one or more searchable data service nodes. For example, one searchable data service host <b>722</b> in a data center may host an instance of coordinator node <b>340</b>, and another host <b>722</b> may host an instance of query TSAR node <b>350</b> and storage node <b>360</b>.

0641In one embodiment, components of a searchable data service node may be instantiated across two or more searchable data service hosts <b>722</b>. In this embodiment, two or more computer systems may constitute one searchable data service node.

0642Searchable data service stores <b>724</b> represent the various data that may be persistently stored by the searchable data service, such as the eID stores <b>236</b>, query index stores <b>234</b>, request logs <b>210</b>, membership maps <b>218</b>, and message logs <b>224</b> illustrated in <figref idref="DRAWINGS">FIG. 6</figref>. Note that, while <figref idref="DRAWINGS">FIG. 12</figref> shows stores <b>724</b> as external to hosts <b>722</b>, in one embodiment, at least a portion of searchable data service stores <b>724</b> may be located on storage within hosts <b>722</b>. In various embodiment, searchable data service stores <b>724</b> may be stored on any type of persistent storage device(s) or storage system(s) within hosts <b>722</b>, within data centers <b>710</b>, remotely located elsewhere on network <b>700</b>, or some combination of the above. Note that a storage node <b>360</b> logically includes at least a local eID store <b>236</b> and a query index store <b>234</b>, along with components that are instantiated on a searchable data service host <b>722</b>. Similarly, coordinator nodes <b>340</b> and query TSAR nodes <b>350</b> may logically include at least some data stored in searchable data service stores <b>724</b>.

0643A client system <b>730</b> may be coupled to the network <b>700</b> via any wired or wireless network connection mechanism. Client systems <b>730</b> may access searchable data service <b>720</b>, via a Web service interface as described above, to create and update searchable indexes for data stored in data stores <b>740</b>, and/or to query the searchable indexes to obtain locators for entities stored in data stores <b>740</b>. Client systems <b>730</b> and the storage devices that store data stores <b>740</b> may be located anywhere on network <b>700</b>. The Web service interface may be provided by a Web services platform (see Web services platform <b>200</b> of <figref idref="DRAWINGS">FIG. 6</figref>, for example) instantiated on one or more server systems coupled to network <b>700</b>, which may or may not reside in data centers <b>710</b> that include other searchable data service <b>720</b> hardware components. Note that the Web services platform may provide redundancy in hardware and software so that the Web services platform is not a single point of failure for the searchable data service <b>720</b>.

0644Note that the underlying architecture, implementation, and operations of searchable data service <b>720</b> are opaque to client systems <b>730</b> and to developers of client applications that are instantiated on client systems <b>730</b> to leverage the searchable data service <b>720</b> as a search frontend for data stores <b>740</b>. Developers may program the search frontends for the client applications in accordance with the exposed Web service interface to the searchable data service.

0645Searchable data service <b>720</b> may scale to store large amounts of data. No special configuration is required to scale the searchable data service <b>720</b>. Heterogeneous machines may be added to the system, and the machines may be detected and added to the searchable data service <b>720</b> automatically. Scaling may be achieved by adding additional hosts <b>722</b> and storage devices to data centers <b>710</b>, and/or by adding new data centers <b>710</b> to the searchable data service <b>720</b>, and not just by adding larger servers.

0646The searchable data service <b>720</b> may be scaled by adding additional hardware to address one or more of, but not limited to, the following: <ul id="ul0093" list-style="none"><li id="ul0093-0001" num="0647"> The number of searchable data service clients. </li><li id="ul0093-0002" num="0648"> The size of a particular searchable index domain for a searchable data service subscriber, and/or the overall size of all domains for all subscribers. </li><li id="ul0093-0003" num="0649"> The size and number of attributes in each searchable data service object. </li><li id="ul0093-0004" num="0650"> The number of requests served (read/write throughput). </li><li id="ul0093-0005" num="0651"> The number of nodes (additional coordinator nodes <b>340</b> may be added for load-balancing, for example). </li><li id="ul0093-0006" num="0652"> Redundancy requirements (how many replicas of a partition are required). </li><li id="ul0093-0007" num="0653"> Availability, consistency, and performance in general. Additional nodes may be added to a data center <b>710</b> and/or additional data centers <b>710</b> may be added to the searchable data service <b>720</b> to improve availability, consistency, and performance of the overall system. As a more specific example, replicating a partition to an additional storage node <b>360</b> within a data center or to storage nodes <b>360</b> in another newly-added data center may provide additional redundancy, increase availability, and improve load-balancing. </li></ul>

0654Rather than requiring particular models of potentially expensive hardware (e.g., server systems) or hardware/software server solutions from particular vendors, searchable data service <b>720</b> may be implemented on relatively inexpensive, heterogeneous commodity hardware from one or more vendors within a data center <b>710</b>. Different types of systems from different vendors may be used as hosts <b>722</b> in the searchable data service infrastructure, with different disk sizes and performance capabilities, different CPU capabilities, RAM capacities, etc, as long as the systems are generally compatible with the other systems in the data center <b>710</b>. In one embodiment, one or more minimum requirements for a host <b>722</b> may be established, but any compatible system that meets the minimum requirements may serve as a host <b>722</b>.

0655Embodiments may support a two-touch data center maintenance model, whereby hosts <b>722</b> may not be repaired, but instead may be replaced, once they fail. By using relatively inexpensive, heterogeneous hardware, the searchable data service <b>720</b> may be scaled inexpensively and rapidly.

0656From the client perspective, searchable data service <b>720</b> functionality and performance should not be affected by system faults such as host <b>722</b>, network, or even data center <b>710</b> failures. The logical and physical architecture of the searchable data service <b>720</b>, as described herein, has no single point of failure. The searchable data service <b>720</b> may withstand the temporary or permanent loss of a machine within a data center <b>710</b> or even an entire data center <b>710</b> without affecting client functionality. The searchable data service <b>720</b> may withstand the random failure of a host <b>722</b>, networking hardware, or even an entire data center <b>710</b> without a significant impact on clients <b>730</b>. The searchable data service <b>720</b> may withstand the intentional shutting down of one or more hosts <b>722</b> in a single data center <b>710</b> without significantly impacting overall operations of the searchable data service <b>720</b>, which for example allows a fleet of hosts <b>722</b> within a data center <b>710</b> to be upgraded if necessary or desired.

0657In one embodiment, searchable data service <b>720</b> may provide global accessibility on network <b>700</b>. In providing global accessibility, the searchable data service <b>720</b> may provide similar latency and throughput performance to clients systems <b>730</b> irrespective of the geographic location of the client system <b>730</b>. Note that a client system <b>730</b> may be coupled to the network <b>700</b> via any wired or wireless network connection mechanism. To assist in providing global accessibility with similar performance experiences for client systems <b>730</b> irrespective of the locations of the client systems <b>730</b>, searchable data service <b>720</b> may be implemented across data centers <b>710</b> that are widely dispersed geographically. A searchable index (domain) of a subscriber that may require global accessibility may then be replicated across the geographically distributed and distant data centers <b>710</b>. Note that a geographically distributed domain may result in a small increase in latency when synchronizing the data across the data centers <b>730</b>.

0000Exemplary System

0658In one embodiment, a host system that implements one or more components of a searchable data service as described herein may include a general-purpose computer system that includes or is configured to access one or more computer-accessible media, such as host system <b>900</b> illustrated in <figref idref="DRAWINGS">FIG. 20</figref>. In the illustrated embodiment, host system <b>900</b> includes one or more processors <b>910</b> coupled to a system memory <b>920</b> via an input/output (I/O) interface <b>930</b>. Computer system <b>900</b> further includes a network interface <b>940</b> coupled to I/O interface <b>930</b>.

0659In various embodiments, computer system <b>900</b> may be a uniprocessor system including one processor <b>910</b>, or a multiprocessor system including several processors <b>910</b> (e.g., two, four, eight, or another suitable number). Processors <b>910</b> may be any suitable processors capable of executing instructions. For example, in various embodiments, processors <b>910</b> may be general-purpose or embedded processors implementing any of a variety of- instruction set architectures (ISAs), such as the x86, PowerPC, SPARC, or MIPS ISAs, or any other suitable ISA. In multiprocessor systems, each of processors <b>910</b> may commonly, but not necessarily, implement the same ISA.

0660System memory <b>920</b> may be configured to store instructions and data accessible by processor(s) <b>910</b>. In various embodiments, system memory <b>920</b> may be implemented using any suitable memory technology, such as static random access memory (SRAM), synchronous dynamic RAM (SDRAM), nonvolatile/Flash-type memory, or any other type of memory. In the illustrated embodiment, program instructions and data implementing desired functions, such as those methods and techniques described above for various nodes of a searchable data service, are shown stored within system memory <b>920</b> as code <b>925</b>. In addition, searchable data service store <b>724</b>C represents the various data that may be persistently stored by the searchable data service, such as the eID stores <b>236</b>, query index stores <b>234</b>, request logs <b>210</b>, membership maps <b>218</b>, and message logs <b>224</b> illustrated in <figref idref="DRAWINGS">FIG. 6</figref>, which in one embodiment may be stored at least in part in system memory <b>920</b> of host(s) <b>900</b>.

0661In one embodiment, I/O interface <b>930</b> may be configured to coordinate I/O traffic between processor <b>910</b>, system memory <b>920</b>, and any peripheral devices in the device, including network interface <b>940</b> or other peripheral interfaces. In some embodiments, I/O interface <b>930</b> may perform any necessary protocol, timing or other data transformations to convert data signals from one component (e.g., system memory <b>920</b>) into a format suitable for use by another component (e.g., processor <b>910</b>). In some embodiments, VO interface <b>930</b> may include support for devices attached through various types of peripheral buses, such as a variant of the Peripheral Component Interconnect (PCI) bus standard or the Universal Serial Bus (USB) standard, for example. In some embodiments, the function of I/O interface <b>930</b> may be split into two or more separate components, such as a north bridge and a south bridge, for example. Also, in some embodiments some or all of the functionality of I/O interface <b>930</b>, such as an interface to system memory <b>920</b>, may be incorporated directly into processor <b>910</b>.

0662Network interface <b>940</b> may be configured to allow data to be exchanged between a host system <b>900</b> hosting a searchable data service node and other devices attached to a network, such as other host systems <b>900</b> hosting other searchable data services nodes and storage devices or systems that may be used to store at least a portion of searchable data service store(s) <b>724</b>D. In particular, network interface <b>940</b> may be configured to allow communications between a host system <b>900</b> and other computer systems on network <b>700</b> hosting a Web services platform <b>840</b> that provides a Web service interface for the searchable data service to client systems <b>730</b> via network <b>700</b>. Network interface <b>940</b> may commonly support one or more wired or wireless networking protocols.(e g., Wi-Fi/IEEE 802.11, or another wireless networking standard). In various embodiments, network interface <b>940</b> may support communication via any suitable wired or wireless general data networks, such as other types of Ethernet network, for example. Additionally, network interface <b>940</b> may support communication via telecommunications/telephony networks such as analog voice networks or digital fiber communications networks, via storage area networks such as Fibre Channel SANs, or via any other suitable type of network and/or protocol.

0663In some embodiments, system memory <b>920</b> may be one embodiment of a computer-accessible storage medium configured to store program instructions and data as described above for implementing one or more components of a searchable data service as described above. However, in other embodiments, program instructions and/or data may be received, sent or stored upon different types of computer-accessible media. Generally speaking, a computer-accessible storage medium may include storage media or memory media such as magnetic or optical media, e.g., disk or DVD/CD coupled to computer system <b>900</b> via I/O interface <b>930</b>. A computer-accessible storage medium may also include any volatile or non-volatile media such as RAM (e.g. SDRAM, DDR SDRAM, RDRAM, SRAM, etc.), ROM, etc, that may be included in some embodiments of computer system <b>900</b> as system memory <b>920</b> or another type of memory. Further, a computer-accessible storage medium may include transmission media or signals such as electrical, electromagnetic, or digital signals, conveyed via a communication medium such as a network and/or a wireless link, such as may be implemented via network interface <b>940</b>.

0000Conclusion

0664Various embodiments may further include receiving, sending or storing instructions and/or data implemented in accordance with the foregoing description upon a computer-accessible storage medium. Generally speaking, a computer-accessible storage medium may include storage media or memory media such as magnetic or optical media, e.g., disk or DVD/CD-ROM, volatile or non-volatile media such as RAM (e.g. SDRAM, DDR, RDRAM, SRAM, etc.), ROM, etc. As well as transmission media or signals such as electrical, electromagnetic, or digital signals, conveyed via-a communication medium such as network and/or a wireless link.

0665The various methods as illustrated in the Figures and described herein represent exemplary embodiments of methods. The methods may be implemented in software, hardware, or a combination thereof The order of method may be changed, and various elements maybe added, reordered, combined, omitted, modified, etc.

0666Various modifications and changes may be made as would be obvious to a person skilled in the art having the benefit of this disclosure. It is intended that the invention embrace all such modifications and changes and, accordingly, the above description to be regarded in an illustrative rather than a restrictive sense.