Upgrade Full-Text Search

Artikkeli
02/28/2023

Applies to: SQL Server Azure SQL Database

SQL Server upgrades full-text search during setup, or when you attach, restore, or copy database files and full-text catalogs from an earlier version of SQL Server.

Upgrade a server instance

For an in-place upgrade, an instance of SQL Server is set up side-by-side with the old version of SQL Server, and data is migrated. If the old version of SQL Server had full-text search installed, a new version of full-text search is automatically installed. Side-by-side install means that each of the following components exists at the instance-level of SQL Server.

Word breakers, stemmers, and filters
Each instance now uses its own set of word breakers, stemmers, and filters, rather than relying on the operating system version of these components. These components are also easier to register and configure at a per-instance level. For more information, see Configure and Manage Word Breakers and Stemmers for Search and Configure and Manage Filters for Search.

Filter daemon host
The full-text filter daemon hosts are processes that safely load and drive extensible external components used for index and query, such as word breakers, stemmers, and filters, without compromising the integrity of the Full-Text Engine. A server instance uses a multithreaded process for all multithreaded filters and a single-threaded process for all single-threaded filters.

Note

SQL Server 2008 (10.0.x) introduced a service account for the FDHOST Launcher service (MSSQLFDLauncher). This service propagates the service account information to the filter daemon host processes of a specific instance of SQL Server. For information about setting the service account, see Set the Service Account for the Full-text Filter Daemon Launcher.

In SQL Server 2005 (9.x), each full-text index resides in a full-text catalog that belongs to a filegroup, has a physical path, and is treated as a database file. In SQL Server 2008 (10.0.x) and later versions, a full-text catalog is a logical or virtual object that contains a group of full-text indexes. Therefore, a new full-text catalog is not treated as a database file with a physical path. However, during upgrade of any full-text catalog that contains data files, a new filegroup is created on same disk. This maintains the old disk I/O behavior after upgrade. Any full-text index from that catalog is placed in the new filegroup if the root path exists. If the old full-text catalog path is invalid, the upgrade keeps the full-text index in the same filegroup as the base table or, for a partitioned table, in the primary filegroup.

Full-text upgrade options

When upgrading a SQL Server instance, the user interface allows you to choose one of the following full-text upgrade options.

Import
Full-text catalogs are imported. Typically, import is significantly faster than rebuild. For example, when using only one CPU, import runs about 10 times faster than rebuild. However, an imported full-text catalog does not use the new word breakers installed with the latest version of SQL Server. To ensure consistency in query results, full-text catalogs have to be rebuilt.

Note

Rebuild can run in multi-threaded mode, and if more than 10 CPUs are available, rebuild might run faster than import if you allow rebuild to use all of the CPUs.

If a full-text catalog is not available, the associated full-text indexes are rebuilt. This option is available for only SQL Server 2005 (9.x) databases.

For information about the impact of importing full-text index, see "Considerations for Choosing a Full-Text Upgrade Option," later in this topic.

Rebuild
Full-text catalogs are rebuilt using the new and enhanced word breakers. Rebuilding indexes can take a while, and a significant amount of CPU and memory might be required after the upgrade.

Reset
Full-text catalogs are reset. When upgrading from SQL Server 2005 (9.x), full-text catalog files are removed, but the metadata for full-text catalogs and full-text indexes is retained. After being upgraded, all full-text indexes are disabled for change tracking and crawls are not started automatically. The catalog will remain empty until you manually issue a full population, after the upgrade completes.

Considerations for choosing a full-text upgrade option

When choosing the upgrade option for your upgrade, consider the following:

Do you require consistency in query results?

SQL Server installs new word breakers for use by Full-Text and Semantic Search. The word breakers are used both at indexing time and at query time. If you do not rebuild the full-text catalogs, your search results may be inconsistent. If you issue a full-text query that looks for a phrase that is broken differently by the word breaker in a previous version of SQL Server and the current word breaker, a document or row containing the phrase might not be retrieved. This is because the indexed phrases were broken using different logic than the query is using. The solution is to repopulate (rebuild) the full-text catalogs with the new word breakers so that index time and query time behavior are identical. You can choose the Rebuild option to accomplish this, or you can rebuild manually after choosing the Import option.
Were any full-text indexes built on integer full-text key columns?

Rebuilding performs internal optimizations that improve the query performance of the upgraded full-text index in some cases. Specifically, if you have full-text catalogs that contain full-text indexes for which the full-text key column of the base table is an integer data type, rebuilding achieves ideal performance of full-text queries after upgrade. In this case, we highly recommend you to use the Rebuild option.

Note

For full-text indexes, we recommend that the column serving as the full-text key be an integer data type. For more information, see Improve the Performance of Full-Text Indexes.
What is the priority for getting your server instance online?

Importing or rebuilding during upgrade takes a lot of CPU resources, which delays getting the rest of the server instance upgraded and online. If getting the server instance online as soon as possible is important and if you are willing to run a manual population after the upgrade, Reset is suitable.

Ensure consistent query results after importing a full-text index

If a full-text catalog was imported when upgrading a SQL Server 2005 (9.x) database, mismatches between the query and the full-text index content might occur because of differences in the behavior of the old and new word breakers. In this case, to guarantee a total match between queries and the full-text index content, choose one of the following options:

Rebuild the full-text catalog that contains the full-text index (ALTER FULLTEXT CATALOGcatalog_name REBUILD)
Issue a FULL POPULATION on the full-text index (ALTER FULLTEXT INDEX ON table_name START FULL POPULATION).

For more information about word breakers, see Configure and Manage Word Breakers and Stemmers for Search.

Upgrade noise-word files to stoplists

When a database is upgraded from SQL Server 2005 (9.x), the noise-word files are no longer used. However, the old noise-word files are stored in the FTDATA\ FTNoiseThesaurusBak folder, and you can use them later when updating or building the corresponding SQL Server stoplists.

After upgrading from SQL Server 2005 (9.x):

If you never added, modified, or deleted any noise-word files in your installation of SQL Server 2005 (9.x), the system stoplist should meet your needs.
If your noise-word files were modified in SQL Server 2005 (9.x), those modifications are lost during upgrade. To re-create those updates, you must manually recreate those modifications in the corresponding stoplist. For more information, see ALTER FULLTEXT STOPLIST (Transact-SQL).
If you do not want to apply any stopwords to your full-text indexes (for example, if you deleted or erased your noise-word files in your SQL Server 2005 (9.x) installation), you must turn off the stoplist for each upgraded full-text index. Run the following Transact-SQL statement (replacing database with the name of the upgraded database and table with the name of the table):
```
Use database;   
ALTER FULLTEXT INDEX ON table  
   SET STOPLIST OFF;  
GO  
```
The STOPLIST OFF clause removes stop-word filtering, and it will trigger a population of the table, without filtering any words considered to be noise.

Backup and imported full-text catalogs

For full-text catalogs that are rebuilt or reset during upgrade (and for new full-text catalogs), the fulltext catalog is a logical concept and does not reside in a filegroup. Therefore, to back up a full-text catalog, you must identify every filegroup that contains a full-text index of the catalog and back each of them up, one by one. For more information, see Back Up and Restore Full-Text Catalogs and Indexes.

For full-text catalogs that have been imported from SQL Server 2005 (9.x), the full-text catalog is still a database file in its own filegroup. The SQL Server 2005 (9.x) backup process for full-text catalogs still applies except that the MSFTESQL service does not exist in SQL Server. For information about the SQL Server 2005 (9.x) process, see Backing Up and Restoring Full-Text Catalogs in SQL Server 2005 Books Online.

Migrating full-text indexes when upgrading a database

Database files and full-text catalogs from a previous version of SQL Server can be upgraded to an existing instance by using attach, restore, or the Copy Database Wizard. SQL Server 2005 (9.x) full-text indexes, if any, are either imported, reset, or rebuilt. The upgrade_option server property controls which full-text upgrade option the server instance uses during these database upgrades.

After you attach, restore, or copy any SQL Server 2005 (9.x) database a newer instance, the database becomes available immediately and is then automatically upgraded. Depending the amount of data being indexed, importing can take several hours, and rebuilding can take up to ten times longer. Note also that when the upgrade option is set to import, if a full-text catalog is not available, the associated full-text indexes are rebuilt.

To change full-text upgrade behavior on a server instance

Transact-SQL: Use the upgrade_option action of sp_fulltext_service
SQL Server Management Studio : Use the Full-Text Upgrade Option of the Server Properties dialog box. For more information, see Manage and Monitor Full-Text Search for a Server Instance.

Considerations for Restoring a SQL Server 2005 (9.x) Full-Text Catalog

One method of upgrading fulltext data from a SQL Server 2005 (9.x) database is to restore a full database backup to a newer instance of SQL Server.

While importing a SQL Server 2005 (9.x) full-text catalog, you can back up and restore the database and the catalog file. The behavior is the same as in SQL Server 2005 (9.x):

The full database backup will include the full-text catalog. To refer to the full-text catalog, use its SQL Server 2005 (9.x) file name, sysft_+catalog-name.
If the full-text catalog is offline, the backup will fail.

For more information about backing up and restoring SQL Server 2005 (9.x) full-text catalogs, see Backing Up and Restoring Full-Text Catalogs and File Backup and Restore and Full-Text Catalogsin SQL Server 2005 (9.x) Books Online.

When the database is restored on a newer instance of SQL Server, a new database file will be created for the full-text catalog. The default name of this file is ftrow_catalog-name.ndf. For example, if you catalog-name is cat1, the default name of the SQL Server database file would be ftrow_cat1.ndf. But if the default name is already being used in the target directory, the new database file would be named ftrow_catalog-name{GUID}.ndf, where GUID is the Globally Unique Identifier of the new file.

After the catalogs have been imported, the sys.database_files and sys.master_files are updated to remove the catalog entries and the path column in sys.fulltext_catalogs is set to NULL.

To back up a database

Full Database Backups (SQL Server)
Transaction Log Backups (SQL Server) (full recovery model only)

To restore a database backup

Example

The following example uses the MOVE clause in the RESTORE statement, to restore a SQL Server 2005 (9.x) database named ftdb1. The SQL Server 2005 (9.x) database, log, and catalog files are moved to new locations on the SQL Server server instance, as follows:

The database file, ftdb1.mdf, is moved to C:\Program Files\Microsoft SQL Server\MSSQL.1MSSQL13.MSSQLSERVER\MSSQL\DATA\ftdb1.mdf.
The log file, ftdb1_log.ldf, is moved to a log directory on your log disk drive, log_drive:\log_directory\ftdb1_log.ldf.
The catalog files that correspond to the sysft_cat90 catalog are moved to C:\temp. After the full-text indexes are imported, they will automatically be placed in a database file, C:\ftrow_sysft_cat90.ndf, and the C:\temp will be deleted.

RESTORE DATABASE [ftdb1] FROM  DISK = N'C:\temp\ftdb1.bak' WITH  FILE = 1,  
   MOVE N'ftdb1' TO N'C:\Program Files\Microsoft SQL Server\MSSQL12.MSSQLSERVER\MSSQL\DATA\ftdb1.mdf',  
    MOVE N'ftdb1_log' TO N'log_drive:\log_directory\ftdb1_log.ldf',  
    MOVE N'sysft_cat90' TO N'C:\temp';

Attaching a SQL Server 2005 database

In SQL Server 2008 (10.0.x) and later versions, a full-text catalog is a logical concept that refers to a group of full-text indexes. The full-text catalog is a virtual object that does not belong to any filegroup. However, when you attach a SQL Server 2005 (9.x) database that contains full-text catalog files onto a newer SQL Server server instance, the catalog files are attached from their previous location along with the other database files, the same as in SQL Server 2005 (9.x).

The state of each attached full-text catalog on SQL Server is the same as when the database was detached from SQL Server 2005 (9.x). If any full-text index population was suspended by the detach operation, the population is resumed on SQL Server, and the full-text index becomes available for full-text search.

If SQL Server cannot find a full-text catalog file or if the full-text file was moved during the attach operation without specifying a new location, the behavior depends on the selected full-text upgrade option. If the full-text upgrade option is Import or Rebuild, the attached full-text catalog is rebuilt. If the full-text upgrade option is Reset, the attached full-text catalog is reset.

For more information about detaching and attaching a database, see Database Detach and Attach (SQL Server), CREATE DATABASE (SQL Server Transact-SQL), sp_attach_db, and sp_detach_db (Transact-SQL).

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