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Shrink a Database

  • Článek

This topic describes how to shrink a database by using Object in SQL Server 2014 by using SQL Server Management Studio or Transact-SQL.

Shrinking data files recovers space by moving pages of data from the end of the file to unoccupied space closer to the front of the file. When enough free space is created at the end of the file, data pages at end of the file can be deallocated and returned to the file system.

Before You Begin

Limitations and Restrictions

  • The database cannot be made smaller than the minimum size of the database. The minimum size is the size specified when the database was originally created, or the last explicit size set by using a file-size-changing operation, such as DBCC SHRINKFILE. For example, if a database was originally created with a size of 10 MB and grew to 100 MB, the smallest size the database could be reduced to is 10 MB, even if all the data in the database has been deleted.

  • You cannot shrink a database while the database is being backed up. Conversely, you cannot backup a database while a shrink operation on the database is in process.

  • DBCC SHRINKDATABASE will fail when it encounters an xVelocity memory optimized columnstore index. Work completed before encountering the columnstore index will succeed so the database might be smaller. To complete DBCC SHRINKDATABASE, disable all columnstore indexes before executing DBCC SHRINKDATABASE, and then rebuild the columnstore indexes.

Recommendations

  • To view the current amount of free (unallocated) space in the database. For more information, see Display Data and Log Space Information for a Database

  • Consider the following information when you plan to shrink a database:

    • A shrink operation is most effective after an operation that creates lots of unused space, such as a truncate table or a drop table operation.

    • Most databases require some free space to be available for regular day-to-day operations. If you shrink a database repeatedly and notice that the database size grows again, this indicates that the space that was shrunk is required for regular operations. In these cases, repeatedly shrinking the database is a wasted operation.

    • A shrink operation does not preserve the fragmentation state of indexes in the database, and generally increases fragmentation to a degree. This is another reason not to repeatedly shrink the database.

    • Unless you have a specific requirement, do not set the AUTO_SHRINK database option to ON.

Security

Permissions

Requires membership in the sysadmin fixed server role or the db_owner fixed database role.

Using SQL Server Management Studio

To shrink a database

  1. In Object Explorer, connect to an instance of the SQL Server Database Engine, and then expand that instance.

  2. Expand Databases, and then right-click the database that you want to shrink.

  3. Point to Tasks, point to Shrink, and then click Database.

    Database
    Displays the name of the selected database.

    Current allocated space
    Displays the total used and unused space for the selected database.

    Available free space
    Displays the sum of free space in the log and data files of the selected database.

    Reorganize files before releasing unused space
    Selecting this option is equivalent to executing DBCC SHRINKDATABASE specifying a target percent option. Clearing this option is equivalent to executing DBCC SHRINKDATABASE with TRUNCATEONLY option. By default, this option is not selected when the dialog is opened. If this option is selected, the user must specify a target percent option.

    Maximum free space in files after shrinking
    Enter the maximum percentage of free space to be left in the database files after the database has been shrunk. Permissible values are between 0 and 99.

  4. Click OK.

Using Transact-SQL

To shrink a database

  1. Connect to the Database Engine.

  2. From the Standard bar, click New Query.

  3. Copy and paste the following example into the query window and click Execute. This example uses DBCC SHRINKDATABASE to decreases the size of the data and log files in the UserDB database and to allow for 10 percent free space in the database.

DBCC SHRINKDATABASE (UserDB, 10);
GO

Follow Up: After you shrink a database

Data that is moved to shrink a file can be scattered to any available location in the file. This causes index fragmentation and can slow the performance of queries that search a range of the index. To eliminate the fragmentation, consider rebuilding the indexes on the file after shrinking.

See Also

Shrink a File
sys.databases (Transact-SQL)
sys.database_files (Transact-SQL)
DBCC (Transact-SQL)
DBCC SHRINKFILE (Transact-SQL)
Database Files and Filegroups