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Resetting Exchange Transaction Log Numbering sequence

Posted on 2009-05-19
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Last Modified: 2012-06-22
Hi

We are running Exchange 2003 SP2.

I have heard that the transaction log numbering sequence is limited to 1million.

http://exchsrvr.org/E2K3/How%20to%20Reset%20the%20Transaction%20Log%20Numbering%20Sequence.htm

The solution to this is to move all log files and checkpoint to another location.

My question is - what act actually resets the log sequence? Is it effectively deleting the checkpoint file so that the logs start from #1 again? What in layman's terms does the chk file do?
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Question by:kam_uk
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Expert Comment

by:FearNoMore
ID: 24428405
What does the .chk file do?
The E##.chk file maintains the checkpoint for the Storage Group. The ## represents the Storage Group number with the First Storage Group file called E00.chk. This checkpoint file keeps track of the last committed transaction. If you are ever forced to perform a recovery, this file contains the point at which the replaying of transaction logs starts.
http://www.msexchange.org/articles/Understanding-Exchange-Information-Store.html
So ineffect the .chk file keeps track of the last transaction log that was committed to the database
What act actually resets the log sequence?
It is the combined process of moving both the log files as well as the .chk file that resets the log sequence
This MS article also talks about resetting the log sequence
http://support.microsoft.com/kb/830408
 
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by:kam_uk
ID: 24495218
Hi

So - if I moved the log files but not the chk file - would this cause database corruption?
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Expert Comment

by:FearNoMore
ID: 24499366
Not in all scenarios will it cause database corruption.....and one cannot be 100% sure.
The chk file keeps track of the last committed transaction log file and the point from where the log files should start the replay process.
The chk file is just like a pointer for transaction log replay.
 
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Author Comment

by:kam_uk
ID: 24510244
Hi FearNoMore...

I was just thinking there would be database corruption because if the logs were moved manually but *not* the checkpoint file, then Exchange would be looking for logs that were no longer there? Whereas if the chk file was moved, then Exchange would essentially just start the log sequence from scratch?

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FearNoMore earned 500 total points
ID: 24515091
kam,
Exchange would definitely look for the logs based on the chk file but if they are not present then it would generate an error and state that the log files could not be replayed since they were not found.
So in effect if the chk file is present and the log files have been moved manually, the database would definitely try to locate the log file that is referred by the chk file....but do remember that there is no actual log file replay taking place and hence there is no data being written into the database.
So since there is no data being written into the database, there is a low possibilty that the database would actually get corrupt.
But all in all, these are all process that are carried out internally by the Extensible Storage Engine (ESE) and hence we cannot be too sure that this will cause database corruption.
You should make sure that the chk file is also moved along with the other log files, to ensure that the log sequence is regenerated.
I hope this makes things clear
 
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