Error log reports database log is truncated right before differential backup

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Error log reports database log is truncated right before differential backup

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Elizabeth.Block

Posted Wednesday, January 16, 2013 12:22 PM

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I've got a SQL Server 2000 system that has many databases in Full recovery with full, diff, and tlog backups. I'm seeing an unusual error that says "Database log truncated". It only shows as an error in the Application Event log. In the SQL Error log it doesn't show it as an error.

Here's the time sequence:
5AM Database log backup of db A
6AM Error: Database log truncated: Database: A
6:01AM Database differential changes backed up: Database: A
So my question is, how/why would the database log be truncated an hour after it has been backed up? I don't know if the Application Event log is erroneously reporting an error or if I have an actual problem.

Any help would be greatly appreciated!

Post #1408033

Lynn Pettis

Posted Wednesday, January 16, 2013 12:44 PM

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Check the differential backup process for the database. It may have a truncate log in it just before the differential backup. Not something I'd want being done.

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Lynn Pettis

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Post #1408039

ALZDBA

Posted Wednesday, January 16, 2013 12:48 PM

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- If the time interval is near constant, just start a sqlprofiler trace to capture all the needed and analyse it afterward.

- how are the backups being created at your systems ? SQLAgent scheduled jobs ?
check all sqlagent jobs to they don't contain a "backup log with truncate only" statement (we've seen that at some of our systems and had to contact the corresponding dev teams to clarify and remove them )

select J.name, suser_sname(J.owner_sid) as Owner, J.enabled, JS.*
from msdb..sysjobs J
inner join msdb..sysjobsteps JS
on JS.job_id = J.job_id
where JS.command like '%backup%truncate%'
order by  Owner, name

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     Jul 13

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Post #1408042

Elizabeth.Block

Posted Wednesday, January 16, 2013 12:52 PM

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Thank you both. I found the issue. Our backup procedure was using Backup log @Database with truncate_only, which truncates the transaction log. Immediately after that it made a differential backup but the truncate_only would invalidate the previous log backups. We'll be fixing this today... Oi Vay!

Post #1408044

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