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Huge DIFF Backup, Normal T-Log Backups


Huge DIFF Backup, Normal T-Log Backups

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homebrew01
homebrew01
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I have a 55 Gig database, and the differential backup for yesterday was 32 Gig !! It was about 5 gig the day before

So, I assumed I could look at my transaction log backups and find a huge T-log backup to identify what time of day something big happened. But my t-logs, every 15 minutes, show 1 backup > 1 gig, and all the others quite small, and similar to other days this week.

What can make a huge Diff backup, without generating huge t-log backup(s) ?



george sibbald
george sibbald
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differential backups contain all the extents that have been touched by updates, therefore a single row update would lead to 64k worth of backup. Educated guess some process or processes occurred that touched a lot of extents leading to a large differential backup but not necessarily a large log backup.

sounds like its time to reset the differential base.

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homebrew01
homebrew01
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The next Full backup is tomorrow morning, so that is good. Puzzled by the huge Diff though. I have trace files from that time period. Not sure the best columns to look at .... I/O ?, but maybe I'll take a look.



Jeff Moden
Jeff Moden
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homebrew01 (4/6/2013)
I have a 55 Gig database, and the differential backup for yesterday was 32 Gig !! It was about 5 gig the day before

So, I assumed I could look at my transaction log backups and find a huge T-log backup to identify what time of day something big happened. But my t-logs, every 15 minutes, show 1 backup > 1 gig, and all the others quite small, and similar to other days this week.

What can make a huge Diff backup, without generating huge t-log backup(s) ?


T-Log backups that occur every 15 minutes happen 96 times a day. If you divide 32 by 96, the average T-Log size is only 0.3333.

--Jeff Moden

RBAR is pronounced ree-bar and is a Modenism for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column.
Although they tell us that they want it real bad, our primary goal is to ensure that we dont actually give it to them that way.
Although change is inevitable, change for the better is not.
Just because you can do something in PowerShell, doesnt mean you should. Wink

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