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Database mirroring : Transaction log space pressure Expand / Collapse
Posted Tuesday, March 5, 2013 10:06 AM
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Last Login: Thursday, November 13, 2014 11:11 AM
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With database mirroring, if the mirror database fails, the transaction log space on the principal database cannot be reused even if we are taking transaction log backup. This mean we need to have enough space for the transaction log to grow or bring mirror database online before the logs fills up the availabale disk space or break the database mirroring.

If we lost our principal database, and we force to switch on the mirror database with the "SET PARTNER FORCE_SERVICE_ALLOW_DATA_LOSS" command. After, the old mirror is now principal with the disconnected status because the old primary stil unavailable.

During this time and until the old principal become mirror and online, do I have a transaction log space pressure on the new principal ?

Post #1426917
Posted Thursday, March 14, 2013 8:34 AM


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Last Login: 2 days ago @ 11:16 AM
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I am not sure I understand exactly what you are asking.

If the mirror fails, the first thing I would do is break the mirror and check my backups to ensure I have no transaction log pressure.

If the principal fails, as you correctly pointed out, the mirror takes over but is advertised as disconnected. In this case as well, I would break the mirror and check my backups to remove the problems associated with transaction log pressure.

The command you posted does exactly what it says on the tin: Allows data loss which is the opposite of what high availability mirroring is about!

A failed mirror imho is no longer a mirror. Break it, fix the problem and reestablish the mirror as soon as you can. With a good backup plan your Transaction Logs remain reasonably small and you no longer have a problem!
Post #1431013
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