Database mirroring goes into synchronizing mode for a long time

Question

Hi,

I am using sql server 2008 with sp3. I have 15 databases which are configured for mirroring on a single instance of sql server. But in 4 databases out of 15, mirroring status is showing as Synchronizing from long time..

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Mark As Answer If My Reply Is Helpful<br/> Thanks<br/> Neeraj Bhandari (MCTS - Sql Server 2008)

Answer 1

http://support.microsoft.com/kb/924686

http://technet.microsoft.com/en-us/magazine/2009.06.sqlqa.aspx

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Best Regards,Uri Dimant SQL Server MVP, http://sqlblog.com/blogs/uri_dimant/

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Answer 2

Hi Neeraj,

If the network link is unreliable between the principal and mirror, you may see the mirroring state switching back-and-forth between SYNCHRONIZING and SYNCHRONIZED
OR 
Chances of principal generating the transaction log faster than the log can be sent to the mirror .. 

By the way to my knowledge Microsoft recommended databases mirroring configuration on instance is not more than 9 databases that's the best practice . That's what i read in one of the article.
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Thanks,Suhas Vallala

Answer 3

Hi Neeraj,

During a database mirroring session, the mirrored database is always in different specific state (the mirroring state). For example, At the start of a database mirroring session, the database is in the SYNCHRONIZING state. The principal server is serving the database, and the mirror is trying to catch up.

According to your description, mirroring status is showing as synchronizing from long time. We need to verify if there are some failures after the synchronizing state is changed synchronized. Or it just be more time for changing the state. There are many factors can affect the database mirroring session. For example, consuming inordinate CPU and/or memory, network traffic , blocked processes or an anti-virus software and so on.

There is a detail about monitoring Database Mirroring, you can review them and check if the mirroring process can run well during a mirroring session.
http://technet.microsoft.com/en-us/library/ms190030.aspx

Thanks,
Sofiya Li

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