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Transaction Log Backups


Transaction Log Backups

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Paul Randal
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Comments posted to this topic are about the item Transaction Log Backups

Paul Randal
CEO, SQLskills.com: Check out SQLskills online training!
Blog:www.SQLskills.com/blogs/paul Twitter: @PaulRandal
SQL MVP, Microsoft RD, Contributing Editor of TechNet Magazine
Author of DBCC CHECKDB/repair (and other Storage Engine) code of SQL Server 2005
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sad, i got this one wrong... Sad
2 options looked very likely ...

http://msdn.microsoft.com/en-us/library/aa173551(SQL.80).aspx
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Thanks Paul. Excellent question.



Jason AKA CirqueDeSQLeil
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jadsmith
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from sql help http://msdn.microsoft.com/en-us/library/ms186865.aspx

Under the full recovery model or bulk-logged recovery model, conventional backups also include sequential transaction log backups (or log backups), which are required. Each log backup covers the portion of the transaction log that was active when the backup was created, and it includes all log records not backed up in a previous log backup.

This indecates that the last answer is correct.
Also it would need to backup anything not backed up in a previous log backup so that it could restore to a point in time after the last log backup.



jshailendra
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Good question..simple one if basics are clear...
Stewart "Arturius" Campbell
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Good question

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john.curran.z3g
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This page suggests that option 2 is correct:

http://msdn.microsoft.com/en-us/library/ms186289.aspx

You can re-create a whole database in one step by restoring the database from a full database backup to any location. Enough of the transaction log is included in the backup to let you recover the database to the time when the backup finished.
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Great question - got it wrong, but caused me to think.

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Lynn Pettis
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Good question. Easy if you understand recovery models and backup/restore processes.

Cool
Lynn Pettis

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Managing Transaction Logs

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Paul Randal
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@jadsmith But the question wasn't about log backups - it was about full backups. Full backups do not affect log backups, nor do they take them into account. A full backup only has to include the transaction log necessary to recover the database consistently to the time when the data-reading portion of the backup completed. It doesn't matter if the transaction log is GBs and there hasn't been a log backup for weeks - the full backup doesn't backup log it doesn't need.

Only a log backup will backup all log generated since the last log backup completes. And only a log backup in the FULL or BULK_LOGGED recovery models will allow the log to clear/truncate.

@john.curran.z3g That wouldn't be enough to recover the database. If there was a long running transaction that started before the full backup did, only backing up the transaction log generated during the backup would not allow the transaction to be rolled back correctly during the restore operation. All the transaction log for that transaction, all the way back to the initial LOP_BEGIN_XACT log record must be backed up for recovery to be able to operate correctly.

See my article in TechNet Magazine for a more full explanation: Understanding SQL Server Backups and also this blog post which gives you code examples you can use to convince yourself of what's going on under the covers: Misconceptions around the log and log backups: how to convince yourself

Thanks

Paul Randal
CEO, SQLskills.com: Check out SQLskills online training!
Blog:www.SQLskills.com/blogs/paul Twitter: @PaulRandal
SQL MVP, Microsoft RD, Contributing Editor of TechNet Magazine
Author of DBCC CHECKDB/repair (and other Storage Engine) code of SQL Server 2005
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