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Stil not clear on sql server Transaction LOG backup

Posted on 2008-06-12
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Last Modified: 2010-03-19
I'm not a DBA but we dont have a DBA here. I think i asked this question maybe 2 yrs ago but i'm still not clear on the procedure for backing up LOG transaction in production environment...

If I remember correctly, 2 jobs ago, the "DBA"...backed up the log every 15 mins and trucated it. So every 15 mins, it was backed up, trucated,.,,backed up, truncated.

Our log file is growing here... not yet very big...1 GB so far....But what is the correct policy/method of do this??
Here it says to truncate it:

http://support.microsoft.com/kb/873235
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Question by:Camillia
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chapmandew earned 2000 total points
ID: 21770386
Truncating it is NOT necessary.  

When you do a log backup, youre removing the inactive poritions of the log....of if you're in full recovery mode, you should be doing log backups....every 15-20 min is a good place to start...but it really depends on the requirements.  You really won't need to shrink the log, so doing your trans log backups every so often will keep your log from growing out of control.  Does that make sense?

BTW..truncating the log makes is so that you can't restore to a point in time...which you'll want to be able to do since you're in full recovery mode already.
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by:Camillia
ID: 21770456
I think I've got it finally..only took maybe 2 yrs :)

I've read that Db should be in full mode in production...this is to be able to retrieve lost data..correct?

If I actually want to shrink the size of the log, i can use shrinkfile ..correct? ( i want to do this in our test environment)
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by:chapmandew
ID: 21770471
If you think you really need to shrink it,then use DBCC SHRINKFILE....do make sure you test it first.

If will help you recover to a point in time...so, if you want to recover to a point in time, you restore your last full backup, last differential backup (if you have one), and any trans logs in order up to the time you want to restore....
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by:Camillia
ID: 21770558
i think i dont understand the second paragraph...

if I backup the log every 15 mins..suppose i start at 1 PM.
At 1:00, i have a backup
At 1:15, i have a log backup
At 1:30 , i have a log backup
At 1:45...something happens and i want to recover. I should restore the backup from 1:30..correct?

-- so backup the transaction log but what is that last differential backup??
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by:chapmandew
ID: 21770593
if you can perform a tail log backup (final tlog backup...the 1:45 backup) then do so...otherwise, you would do this:

restore your full backup from 1
restore your tlog backups from 1:15 and 1:30.  If the 1:30 is the last tlog bkup you have, then you're done.  If you have the tlog backup from 1:45, you can restore up to the point in time of the error....say it happend at 1:40, you can restore up to 1:39 or so.
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by:Camillia
ID: 21770642
One last question....you say it not needed to shrink the tlog
that link above has:
"To recover from a situation where the transaction logs grow to an unacceptable limit, you must reduce the size of the transaction logs. To do this, you must truncate the inactive transactions in your transaction log and shrink the transaction log file."

What if I shrink , but still have the tlogs...can I still recover the DB by using the tlogs? I would think the answer is yes...
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by:Camillia
ID: 21770773
i do get it. Amazing. Thanks.
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