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We are running six transaction log backups every day on our SQL Server with three hours gap for each succeeding pair. I have noticed the 'data size change' column of the transaction log backups on the server to show 630%, -21%, 0%, 2%, 3%, and -83%. I don't know what these values mean. Sometimes these go up to 1854%. Can anyone tell me what these values mean, and if we should be worried about them?

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Transaction logs for what exactly? I'm assuming SQL Server, but clarification would be nice. – Ben Pilbrow May 10 '11 at 21:47
Yes that's right. Transaction Logs for a SQL Server. – neeecowlaaah May 10 '11 at 23:21
up vote 4 down vote accepted

After looking around, it's hard to find good info on this, so what I'm giving you is a best guess based on what I can research. I would say that the data size change is the change in data since the last backup. You can see the larger percentages after a reindexing of the database (among other things), as all of those are captured as transactions in the log. Subsequent backups would show a reduction in the amount backup up as the transactions stabilized, hence the negative percentages. I don't think this is anything to be worried about. I'll give you some links on what I'm basing this off of.

Log-Shipping and DB FULL backup in-parallel increases size of sub-sequent trn log file size after the backup

How do I reduce transaction log backup size after a full backup?

BACKUP (Transact-SQL)

A transaction log grows unexpectedly or becomes full on a computer that is running SQL Server

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Thanks! Yes that makes a lot of sense. I have noticed that most of the transaction log backups that started after (not exactly on the time) the Full backup finished have huge data size changes. Thanks a lot - couldn't vote you up yet as I'm new here. – neeecowlaaah May 11 '11 at 4:02

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