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Cranky Bit

Because sometimes technology makes you cranky

How to Clear Stubborn Transaction Logs in Microsoft SQL Server

17 February 2017

Clearing transaction logs in SQL databases can be a pain when the database sometimes gets huge and it can’t ever clear the logs even after backup. How to clear those stubborn transaction logs?

In older versions of SQL server (such as MSSQL 2008 or older), I recommended the method of backing up the database with TRUNCATE_ONLY and then running SHRINKFILE(), so something like this:

USE DatabaseName
DBCC SHRINKFILE( TransactionLogName, 200 )
DBCC SHRINKFILE( TransactionLogName, 200 )

The TRUNCATE_ONLY has became a deprecated solution, however, and actually doesn’t work in 2012 and beyond. However, if you still run a BACKUP LOG command, it will typically work well. Here’s an example script that helps automate the saving of the file with a date/time stamp so you can save the .trn files.

DECLARE @trnpath NVARCHAR(255) = 
    N'c:\path\to\backup\file_' + 
    CONVERT(CHAR(8), GETDATE(), 112) + '_' + 
    REPLACE(CONVERT(CHAR(8), GETDATE(), 108),':','') + '.trn';
USE DatabaseName
DBCC SHRINKFILE( TransactionLogName, 200 );

Run this 2 or 3 times and normally the log will finally shrink.

Why the need to run it multiple times? Because there are segments of the file that are in use or marked as not ready to be removed. You can observe this activity with the LOGINFO() command:

DBCC LOGINFO('DatabaseName')

Any records with a status of 2 are portions of the log that are active or otherwise incapable of being truncated as of yet. I’ve heard of databases sometimes being really stubborn and not letting go of these, but often I’ve seen this method will work on MSSQL 2012 and beyond.