Why Is a SQL Log File Huge and How Should I Deal with It?

This article explains why a SQL log file is huge and how to deal with it.

By Kelvin Galabuzi

What Is a SQL Server Log File?

A SQL Server log file is a transaction log file that records all database transactions and modifications. In SQL terms, this log file records all the INSERT, UPDATE, and DELETE query operations performed on a database.

SQL Server typically issues a 9002 error if the log fills up when the database is online or in recovery. In this case, the database can only be read but not updated.

Why the SQL Log File Is Huge

There are a few possible reasons why a SQL log file is huge:

Log file not getting truncated; This is common when the transaction log backups are not performed for your database, especially when the database is in full or bulk-logged recovery models.
Setting the database in full recovery; Full recovery model means a database can be restored to a specific point, thus increasing the transaction log file's size.
Large database transactions, such as importing large amounts of data, can lead to a large transaction log file.
Transaction log backups not happening fast enough causes the SQL log file to become huge.
SQL log files also enlarge due to incomplete replication or availability group synchronization.

How to Deal with a Huge SQL Log File

There are a few things you can do to deal with a huge SQL log file:

Back up the Transaction Log Backup: When your database uses a full or bulk-logged recovery model, you should back up the transaction log to prevent it from filling. This performs log truncation.
Shrink the Log File Size: When the transaction log has unused space, you can shrink a log file to create some space.
Increase the Log File Size: You can increase the log file size. The maximum size for a log file is two terabytes.
Enable Autogrowth: Autogrowth enables the SQL Server to expand the size of database files when they run out of space. Files can grow by a specific size.

Free up Disk Space: Sometimes, the transaction log file fills up the disk space. You can free up disk space or move the log file to a different disk to solve this issue.
Monitor the SQL Transaction Log File: You can create alerts that monitor the log space usage using tools such as System Center Operations Manager (SCOM). In addition, you can use dynamic management views (DMV) in SQL, such as the sys.dm_db_log_space_usage, to monitor space usage of the transaction log of a database.