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Can lots of User Connections cause high CPU use


Can lots of User Connections cause high CPU use

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peterhe
peterhe
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Are you sure it is the % Privileged Time >90%? That means CPU is busy in kennel mode, e.g. using operating system services, processing IOs, Paging Memories to disk, etc.

What is the % User time?



Rahim+971-501387269
Rahim+971-501387269
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http://social.msdn.microsoft.com/Forums/en-US/sqlnetfx/thread/942fe3d4-141a-486a-afdf-53f079d3a4d3

This is an issue that is new in SQL Server 2005, and is only exposed under specific conditions – namely,
the use of the x64 version of SQL Server 2005 and the execution of large ad hoc query batches. Unfortunately, the memory that is used to store the execution plans for those ad hoc queries is not trimmed aggressively enough in the x64 version, and as a result we see more and more connections having to wait for memory allocations before they can continue. If any connection is suspended for more than 30 seconds, the application terminates the connection by reporting that the command currently executing has timed out.

This issue has been previously identified and is fixed in the upcoming service pack release (SP2) for SQL Server 2005, the Community Technology Preview (CTP) release of which is available today, and is confirmed to fix the issue in your environment.

Possible Solutions:

1. Sp2

2. create a job that manually frees the memory that is being consumed by query plans through the use of the
DBCC FREEPROCCACHE command. The documentation for this command states that “freeing the procedure cache causes,
for example, an ad hoc SQL statement to be recompiled instead of reused from the cache.”
(http://msdn2.microsoft.com/en-us/library/ms174283.aspx)
We have not tried out the second solution so far.

3.Change the Max Degree of Parallelism argument at the server/instance level, to something less than # or processors.
GilaMonster
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Please note: 4 year old thread.

Also, ad-hoc queries and plan cache has nothing to do with sleeping connections. Sleeping connections are ones waiting for input from the application, they are doing nothing.
Max degree of parallelism has nothing to do with sleeping connections, nor with plan memory

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

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