Word breakers and stemmers (fdhost.exe) – Each language has its set of word breakers.You can run following query in order to get an overview of the filters defined by default: They will be used, for instance, in order to remove any embedded formatting on the text of a MS Word document. Filters – (fdhost.exe) – they are specific by document type and allow the extraction of text data from various data types like varbinary, image or xml.Protocol Handler Thread – (fdhost.exe) – this thread pulls data from memory for further processing and accesses data from a user table. Filter Daemon Manager – (sqlserv.exe)– this thread monitors the status of the fdhost.exe daemon service.Full-Text Indexer – (sqlserv.exe)– This thread builds the structure used to store index tokens.It compiles and runs full-text queries and takes stoplists and thesaurus files into account before sending back results sets for these queries. Full-Text Engine – (sqlserv.exe)– can be seen as part of the Query Processor.The query results is matched against the full-text index. Query Processor thread – (sqlserv.exe)– thread that compiles and executes T-SQL queries and send Full-Text search to the Full-Text Engine twice: once at compilation and once during query execution.StopLists – in sqlserv.exe – objects that contain list of common words that can be ignored as they are not significant for a lookup (e.g.Thesaurus files – (sqlserv.exe)– files that contain synonyms of search terms.Full-Text gatherer – in sqlserv.exe – a thread responsible for scheduling and driving index population so as for monitoring.User tables – (sqlserv.exe) – tables for which a full-text index exists.This means that the entire Full-Text Search feature is spread across these two processes: fdhost.exe and sqlserv.exe and that some components of this feature interact with each other’s. It’s also called to analyze Full-Text queries, including word breaking and stemming (see below for more info). Fdhost.exe process will access, filter and tokenize user data in order to actually build Full-Text indexes. It will exchange data with SQL Server service (sqlservr.exe) via shared memory or a named pipe. It is started by a service launcher called MSSQLFDLauncher for security concerns. This process will be referred in following as the “filter daemon host“. Notice that, already at SQL Server installation, we can tell that this feature is special as the installer defines a daemon service called “fdhost.exe”. Now that we know what the purpose of Full-Text Search feature is, let’s invest some time in the understanding of how it works. Once we are done with theoretical aspects, we’ll then focus on some practical aspects in order to use and maintain this feature: we will see how to create a Full-Text indexed table, how to list out which tables have a Full-Text index and on which columns and much more We’ll even go through an illustrative example. In this part, we will define some concepts and use them to understand how a Full-Text Index is built and maintained. In the following sections, we will first take some time to understand overview how a Full-Text Search feature works. The building and usage of Full-Text indexes is always performed in a specific language context like English or French. These columns can be of following data types: This index can be built on the top of one or more columns for a particular table. This feature lets users and application run character-based lookups efficiently by creating a particular type of index referred to as a Full-Text Index. Microsoft SQL Server comes up with an answer to part of this issue with a Full-Text Search feature. This means it won’t be fast in every case, even if an index is created for considered column. For instance, a LIKE operator will lead SQL Server to scan the whole table in order to pick up values that meet the expression next to this operator. In most cases, we will use clustered and non-clustered indexes to help a query go faster, but these kinds of indexes have their own limitations and cannot be used for fast text lookup.
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