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Exchange and transaction logs

Posted on 2011-09-10
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Last Modified: 2012-05-12
Hello

My understanding is that Exchange will write information to transaction logs/memory first as an action takes place and then write this information to the database when it has some spare time. For instance, UserA deletes an item in their inbox. Exchange first writes this change to the current transaction log/memory, then when it is less busy, it will write this change to the ESE database itself. Also, usually, Exchange will use the data in memory to write to the database, as opposed to the transaction logs. The logs are actually used only if the server crashes and the memory is no longer there. If the transaction log itself is corrupt/not present, this will be a problem because the ESE db will be out of sync.

Do I have the basic idea correct?

My question is - how long does ESE usually lag behind transaction logs/memory? Are we talking about a few mins, an hour, a day etc?

And, for a database that is mounted, is is possible to tell (using an ESEutil command, for example) what the last log file that was commited was?

Applies to Exchange 2007 and 2010.
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Question by:neil4933
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I am not sure this is what you meant by what you wrote so sorry if I am just repeating you

The information store will try to reserve as much memory as possible since memory access is much faster than disk

every change is written simultaneously to the memory and to the transaction logs (this is called write-ahead logging).

then changes are committed from the memory to the database and updated in the checkpoint file.

So yes, in active copy of the database, logs are only used in a crash.

The lag is surely not hours not even minutes, I would say seconds but I don't think this is documented anywhere
and no there is no way of knowing, on a mounted database, which log files are now committed and which not
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