SQL Server native log backup running every 5 minutes

Question

What will happen if SQL Server native log backup is running ever 5 minutes and due to high active transaction the backup was not able to complete in 5 minutes ?

Will the next log backup be initiated after 5 minutes or will it be waiting for the log backup to complete.

I searched for resources online but couldn't get a proper content. Any reference will be much appreciated Thanks.

Answer 1

Will the next log backup be initiated after 5 minutes or will it be waiting for the log backup to complete.

If the log backup is run by SQL Server Agent

If the scheduled time comes up and the prior instance of the job is still running, it will postpone until the next scheduled time. Two instances of the same job can not run at the same time.

If the log backup is run by some other scheduler software

You'll have to check with your vendor's documentation or support team, but I can't imagine any software allowing this to behave any differently than SQL Server Agent, unless they have an option to not skip collisions and queue them up, and you have enabled that option.

Answer 2

BACKUP LOG requires a lock on the database. If two sessions attempt to backup the log at the same time, one will be blocked waiting on LCK_M_U on the Database until the first completes.

And BACKUP LOG only backs-up the log records that were written before it started. If more transactions occur while BACKUP LOG is running, they are left for the next log backup to deal with.