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Home » SQL Server 2005 » SQL Server 2005 Performance Tuning » clearing SQL cache
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vkkrishn
Posted Tuesday, April 06, 2010 10:58 PM
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Hello,
We have our application running on sql server 2005. Recently we started slowing down of the database and timeouts. Once we clear the SQL cache, it turns normal again. What all can be the causes of this issue we are facing. And what can we do to avoid this. Please help!
Post #898151
SQLRNNR
Posted Wednesday, April 07, 2010 1:22 AM


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Are you getting any error messages along with the slowdown or are you just experiencing general slowness? Are you seeing application timeouts?


Jason AKA CirqueDeSQLeil
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Dave Ballantyne
Posted Wednesday, April 07, 2010 1:31 AM


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Do you mean the procedure cache (DBCC FREEPROCCACHE) or the buffer cache(DBCC DROPCLEANBUFFERS) ?

Im guessing the former, could potentially be parameter sniffing http://www.sqlpointers.com/2006/11/parameter-sniffing-stored-procedures.html


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Post #898240
ALZDBA
Posted Wednesday, April 07, 2010 6:29 AM


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What service pack is your sql2005 on ?

Please post the result of 
select @@version

or
Select Serverproperty( 'ProductVersion' ) as ProductVersion 
 , Serverproperty( 'ProductLevel' ) as ProductLevel 
 , Serverproperty( 'ResourceLastUpdateDateTime' ) as ResourceLastUpdateDateTime 
 , Serverproperty( 'ResourceVersion' ) as ResourceVersion 
 , Serverproperty( 'Edition' ) as Edition 
 , Serverproperty( 'EditionID' ) as EditionID

What action did you perform to "clear the cache" ?

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Post #898417
Paul White
Posted Wednesday, April 07, 2010 6:32 AM


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Dave Ballantyne (4/7/2010)
Do you mean the procedure cache (DBCC FREEPROCCACHE) or the buffer cache(DBCC DROPCLEANBUFFERS) ?

Im guessing the former, could potentially be parameter sniffing http://www.sqlpointers.com/2006/11/parameter-sniffing-stored-procedures.html

I like guessing games
My guess is procedure cache bloat due to ad-hoc queries.
http://blogs.msdn.com/sqlprogrammability/archive/2007/01/23/4-0-useful-queries-on-dmv-s-to-understand-plan-cache-behavior.aspx
DBCC FREESYSTEMCACHE('SQL Plans');


Paul White
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Post #898419
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Posted Wednesday, April 07, 2010 11:01 AM


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vkkrishn,
Do you have any of the information / answers for the questions asked?


Jason AKA CirqueDeSQLeil
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Dave Ballantyne
Posted Wednesday, April 07, 2010 3:07 PM


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Paul White NZ (4/7/2010)
My guess is procedure cache bloat due to ad-hoc queries.


Which reminds me , ive still got a half finished blog on forced parametrization hanging around.


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Post #899023
Paul White
Posted Wednesday, April 07, 2010 6:34 PM


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Dave Ballantyne (4/7/2010)
Paul White NZ (4/7/2010)
My guess is procedure cache bloat due to ad-hoc queries.

Which reminds me , ive still got a half finished blog on forced parametrization hanging around.

Well get on with it then!!!


Paul White
SQL Server MVP
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Post #899172
sam.alexander
Posted Friday, April 09, 2010 10:23 AM


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vkkrishn (4/6/2010)
Hello,
We have our application running on sql server 2005. Recently we started slowing down of the database and timeouts. Once we clear the SQL cache, it turns normal again. What all can be the causes of this issue we are facing. And what can we do to avoid this. Please help!


We ran into this exact situation not long ago, and what I found was SQL created different cached execution plans based on the parameters we were passing into a procedure, and in some cases the cached execution plan, though ran speedy for some parameters ran very inefficiency with other parameters.

Once I found the troublesome procedure my fix was to view the execution plan and create a few indexes so the same, more efficient cached execution plan was created regardless of parameters used, which worked.

The first thing you need to do is determine what process is taking the longest to run. You may be able to monitor your processes and see which ones are taking a long time to run and go from there.

Let me know if you need more details and I can send you some of what we did to find the troublesome procedure then remedy the latency.

Take care --

Sam
Post #900697
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