The following tables show an overview of all the available search components and search databases. For more information about how search components and databases interact, see the Search architectures for SharePoint Server 2013 Preview technical diagram.

Search components

Search databases

The crawl component crawls the content sources. You can crawl a wide variety of content sources, for example file shares, SharePoint content, line of business applications and many more. To retrieve information, the crawl component connects to the content sources by invoking the appropriate indexing connector or protocol handler. After retrieving the content, the crawl component passes crawled items to the content processing component.

For more information about crawling content sources, see Plan crawling and federation in SharePoint Server 2013.

The content processing component processes crawled items and sends these items to the index component. The content processing component performs operations such as document parsing and property mapping. It also performs linguistics processing such as language detection and entity extraction. The component transforms crawled items into artifacts that are included in the search index. The content processing component also writes information about links and URLs to the link database. In turn, the analytics processing component writes information related to the relevance of these links and URLs to the search index through the content processing component.

For more information about content processing, see Plan crawling and federation in SharePoint Server 2013.

The analytics processing component analyzes crawled items, which is referred to as search analytics, and how users interact with search, which is referred to as usage analytics. Examples of search analytics are links, anchor texts and metadata. An example of usage analytics is the number of times an item is viewed. The analytics processing component analyzes search analytics and usage analytics. Search analytics information is stored in the link database and usage analytics information in the analytics reporting database. For more information, see Overview of analytics processing in SharePoint Server 2013.

The index component is the logical representation of an index replica. In the search topology, you have to provision one index component for each index replica. The index component receives processed items from the content processing component and writes those items to an index file. Index files are stored on a disk in an index replica.

The index component receives queries from the query processing component and returns result sets.

You can divide the search index into discrete portions, called index partitions. Each index partition holds one or more index replicas. The search index is the aggregation of all index partitions.

For more information about the search schema and the search index, see Overview of the search schema in SharePoint Server 2013.

The query component analyzes and processes queries and results. When the query processing component receives a query, it analyzes and processes the query to optimize precision, recall and relevance. The processed query is submitted to the index component. The index component returns a result set based on the processed query to the query processing component, which in turn processes that result set, before returning it to the front-end.

For more information, see Plan to transform queries and order results in SharePoint 2013.

The search administration component runs the system processes for search. This component performs provisioning, which is to add and initialize instances of the other search components.

The crawl database stores tracking information and details about crawled items. For example, it stores information about the last crawl time, the last crawl ID and the type of update during the last crawl.

The link database stores information extracted by the content processing component. It also stores information about the number of times people have clicked on a search result. The information is stored unprocessed; the analytics processing component performs the analysis.

The analytics reporting database stores the results of usage analytics and extracts information from the link database when it is required.

The search administration database stores search configuration data and the access control list (ACL) for the crawl component. There can be only one search administration database per search service application.