Why is the First Transaction Log backup of the day huge

I noticed that the first transaction log backup of the day, at 0700 is like 3GB. We run a full backup each night at 22:00. We are a 9-5 shop so there is no real activity overnight. We take TLog backups hourly during the day and they average around 30 MB. How can I find out why this first log backup is so big?
Thanks!

That depends on what is happening in the night.

• If you have additional maintenance jobs (index rebuilds, index reorganizations, statistics updates) then you possibly have a lot of changes occurring.

• If you are also importing large amounts of data, then that is another possible source of changes.

• Deleting data is also a modification and will be logged.

A database that is truly dormant will normally not have huge transaction log backups.

You may also want to consider either taking a second full backup and a transaction log backup after the nightly maintenance, and use that backup as your base for the day's log backups solely to avoid the massive post-maintenance log file, or to just postpone the full backup and subsequent transaction log backups till after the maintenance.

StackExchange Database Administrators Q#187894, answer score: 7