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Kevin Kline

MIRRORING THROTTLES BACKLOG

For some reason, the title of this blog post makes me grin because it evokes a mental image of one guy trying to comically strangle another guy.  But I digress…

 

Speaking at a user group meeting recently, an attendee asked whether the mirroring process had any capability to speed up or slow down its workload according to the amount of work waiting on it.  I cast around for an answer to this and my friend, Kalen Delaney, already had the answer.  She already has an answer for most any question on SQL Server, but again I digress.  She got her answer from Peter Byrne, a Microsoft program manager and member of the SQL Server Storage Engine team.

 

Peter says…”There is a throttling heuristic used by mirroring to try to keep the backlog from getting too large on the mirror.  Essentially, at commit time SQL Server may pause briefly if it determines the REDO queue on the mirror is getting large enough that failover time would be significantly affected.”

 

You can find more details about this process in the white paper:

 

http://www.microsoft.com/technet/prodtechnol/sql/2005/technologies/dbm_best_pract.mspx

 

And while we’re at it, don’t forget to investigate Kalen’s new DVD at http://sqlblog.com/blogs/kalen_delaney/archive/2008/01/24/did-you-know-my-dvd-is-now-orderable.aspx#4722.  Not only is it a great value at any price with fantastic content, it’s only $19.95 plus $3 for S/H, which, when you think of it is incredibly cheap.  Taking a MOC (Microsoft Official Curriculum) class is measured in the thousands of dollars.  Kalen’s content, which is some of the best available, is so affordable!

Published Friday, May 02, 2008 4:07 AM by KKline

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Adam Machanic said:

If anyone wants to see this in action, set up mirroring, open the Mirroring Monitor and create an index on a big table.  Unless you have a superfast network, you'll see the buffers start to fill up and the process will sit there and wait until everything clears out...

May 2, 2008 11:33 AM
 

KKline said:

Thanks for the note, Adam.  That's excellent input!

-Kev

May 14, 2008 12:04 PM

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About KKline

Kevin Kline is a well-known database industry expert, author, and speaker. Kevin is a long-time Microsoft MVP and was one of the founders of PASS, www.sqlpass.org.

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