DB Log File Space

Summary

Monitors the space available on the log files and on the media hosting the log files. The space available on the media hosting the log files are only included as part of the space available if auto grow is enabled for at least one of the files.

Causes

An unhealthy state is caused by having low available space across all log files. Low available space can be caused by:

• Inadequate file configuration settings (size, max size, auto grow, etc.)

• Inadequate space left on media

• Lack of periodic regular backups

• Log not truncating

Use the following links to view the performance data: DB File Log Free Space Performance Data

This monitor aggregates the space available for each log file within a database depending on each file’s configuration:

No Auto Grow

For a file that has no auto grow, available space would be the difference between the initial size for a file and the used space.

Auto Grow Enabled

In addition to the difference between the file size and the used space, the available space for files with auto grow enabled would be the minimum of either the difference between the max size and the file size and the free space left on disk.

Low available space for database files that have auto grow could mean that the file is approaching the limits of the hosting logical drive. For files with auto grow enabled with a max size, low available space could also mean that the file is approaching the max size specified for a file.

The available space calculations also take into account that the file can also fail to grow if the growth amount of the file is greater than the amount left on disk and that the file cannot grow if the difference between the max size and the current file size is less than the growth amount. In these situations, available free space left on disk is not included as part of the available space because we cannot grow any longer.

Resolutions

This issue may be resolved by either:

• Increasing the allocated size for log files if auto grow is disabled

• Increasing the max size value for a log file if auto grow is enabled

• Enabling auto grow for at least one file

• Moving log files to another drive with more free space if growth space is limited

• Performing regular backups of log files for FULL and BULK-LOGGED recovery modes

• Investigate why log is not getting truncated:

  • Long open running active transactions

  • Long running backup operations

  • Replicated transaction open for a long time (Transactional Replication)

  • Mirror lagging behind principal server (Database Mirroring)

• Modifying the thresholds for this monitor to suit the workload

• Alternatively if log file available space is not a concern for the database:

  • Disable this monitor for this specific database or all databases

See SQL Server Books Online: Files and File Groups Architecture