SQL Server Shrink Log File

Kailash Chandra Behera | Wednesday, September 23, 2020

Introduction

SQL shrink log file helps to compress the database and reduce SQL server log file size which leads reclaim spaces by recovering spaces. This blog, guides to shrink database log file (MSSQL shrink log file) to recovers space in SQL Server using Microsoft SQL Server Management Studio and TSQL shrink database query.

Getting Started

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 the end of the file can be deallocated and returned to the file system.

Note that 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.

Demonstration

This demonstration is conducted in SQL Server Management Studio 2017. Here we will discuss how to shrink the SQL server in two different ways. Using SSMS options and SQL query.

Shrink Database Log File using SSMS (MSSQL shrink log file)

  1. Open SQL Server Management Studio and login to your SQL instance.

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

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

  4. Point to Tasks, point to Shrink, and then click Files.

  5. Select the file type and file name.

  6. Optionally, select the Release unused space check box. This option causes any unused space in the file to be released to the operating system and shrinks the file to the last allocated extent. This reduces the file size without moving any data.

  7. Optionally, select the Reorganize files before releasing unused space check box. If this is selected, the Shrink file to value must be specified. By default, the option is cleared. This causes any unused space in the file to be released to the operating system and tries to relocate rows to unallocated pages.

  8. Optionally, enter the maximum percentage of free space to be left in the database file after the database has been shrunk. Permissible values are between 0 and 99. This option is only available when Reorganize files before releasing unused space is enabled.

  9. Optionally, select the Empty file by migrating the data to other files in the same filegroup check box. It moves all data from the specified file to other files in the filegroup. The empty file can then be deleted. This option is the same as executing DBCC SHRINKFILE with the EMPTYFILE option.

  10. Click OK.
Parameter Description

  1. Database
    Displays the name of the selected database.

  2. File type
    Select the file type for the file. The available choices are Data and Log files. The default selection is Data. Selecting a different filegroup type changes the selections in the other fields accordingly.

  3. Filegroup
    Select a filegroup from the list of Filegroups associated with the selected File type above. Selecting a different filegroup changes the selections in the other fields accordingly.

  4. File name
    Select a file from the list of available files of the selected filegroup and file type.

  5. Location
    Displays the full path to the currently selected file. The path is not editable, but it can be copied to the clipboard.

  6. Currently allocated space
    For data files, displays the current allocated space. For log files, displays the current allocated space computed from the output of DBCC SQLPERF(LOGSPACE).

  7. Available free space
    For data files, displays the current available free space computed from the output of DBCC SHOWFILESTATS(fileid). For log files, displays the current available free space computed from the output of DBCC SQLPERF(LOGSPACE).

  8. Release unused space
    Cause any unused space in the files to be released to the operating system and shrink the file to the last allocated extent, reducing the file size without moving any data. No attempt is made to relocate rows to unallocated pages.

  9. Reorganize pages before releasing unused space
    Equivalent to executing DBCC SHRINKFILE specifying the target file size. When this option is selected, the user must specify a target file size in the Shrink file to box.

  10. Shrink file to
    Specifies the target file size for the shrink operation. The size cannot be less than the current allocated space or more than the total extents allocated to the file. Entering a value beyond the minimum or the maximum will revert to the min or the max once the focus is changed or when any of the buttons on the toolbar are clicked.

  11. Empty file by migrating the data to other files in the same filegroup
    Migrate all data from the specified file. This option allows the file to be dropped using the ALTER DATABASE statement. This option is equivalent to executing DBCC SHRINKFILE with the EMPTYFILE option.

SQL Shrink DB using the T-SQL query

The following SQL query helps to shrink the database. This example uses DBCC SHRINKDATABASE to decreases the size of the data and log files in the database and to allow for 10 percent free space in the database. 

USE database_name;
GO
DBCC SHRINKFILE (database_logfilename, 7);  
GO

Shrink Log SQL Server

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Summary

In the above, we learn how to string SQL server database log file using two different ways (using SSMS and T-SQL query). I hope you have enjoyed it a lot.

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