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Set recovery model to full.  What to do with existing log (.ldf) files?

Posted on 2016-09-08
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Last Modified: 2016-09-08
A consultant changed the recovery model from full to simple for our production SQL databases.  I would like to set the recovery model back to full.  However, the log files (.ldf) have a date/time which is the same as the .mdf files.  I'm not sure what to do with the log files.  Should I delete them or leave them alone?  I wonder why the log files have the same date/time as the the .mdf files if the recovery model is set to simple?  Thank you.Screenshot of date/time for mdf and ldf files
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Question by:davidrobertbristow
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Expert Comment

by:Scott Pletcher
ID: 41790081
DON'T EVER DELETE LOG FILES!

Log files are still needed, even in simple mode.
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Scott Pletcher earned 2000 total points
ID: 41790084
Instead, simply change the mode back to FULL and take a full database backup as soon as you can.  Then start taking regular log backups again, as you would any time a db is in FULL recovery model.  That's all you need to do, nothing extra/special.
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Author Comment

by:davidrobertbristow
ID: 41790090
Can I change the recovery model back to full during production or does it need to be done off-hours?
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Expert Comment

by:Scott Pletcher
ID: 41790110
You can do it any time.  

But it won't actually provide any additional recovery possibilities until you've taken a full db backup.  That is, the point of full recovery mode is to allow you to recover changes lost if the db fails; the log file is used "forward recover" (as it's called), i.e. reapply data, to the db.  

But you can't use the log to forward recover until you have a full db backup from which to work.  And a full backup made when in SIMPLE recovery mode won't work.  You have to have a full backup made after the db was put back into full mode to use as a valid starting recovery point.
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Author Comment

by:davidrobertbristow
ID: 41790114
I understand.  Set the recovery mode to full.  Then, take a full DB backup to start the log file chain.  Thank you!
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