SQL Server: How to shrink your DB Logs (without putting your job at risk)

This post is mostly a reminder for myself 🙂

When your SQL Server DB log files are growing and your disk is close to being full (or, as it happened this morning, fill up completely thus preventing any DB operation whatsoever, bringing the affected system down!) you need to shrink them.

What this means, basically, is that you create a backup (do NOT skip that!) and then you delete information that allows you to recover the database to any point in time before the backup. That’s what SET RECOVERY SIMPLE & DBCC SHRINKFILE do. And since you kept a backup, you no longer need this information. You don’t need it for operations after the backup though, that’s why we go back to full recovery mode with SET RECOVERY FULL at the end.

So what you need is to login to your SQL Server with admin rights and:

USE DatabaseName
GO
BACKUP DATABASE DatabaseName
TO DISK = 'C:\dbbackup\DatabaseName.bak'
   WITH FORMAT,
      MEDIANAME = 'DatabaseNameBackups',
      NAME = 'Full Backup of DatabaseName';
GO
ALTER DATABASE DatabaseName SET RECOVERY SIMPLE;
GO
CHECKPOINT;
GO
DBCC SHRINKFILE ('DatabaseName_Log', 10);
GO
ALTER DATABASE DatabaseName SET RECOVERY FULL;
GO

Notice the 10 there -that’s the size, in MB, that the DB Log file will shrink to. You probably need to change that to match your DB needs. Also, the DatabaseName_Log is the logical name of your DB Log. You can find it in the DB properties. You probably also need to change the backup path from the example C:\dbbackup\DatabaseName.bak.

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