Duty Free!!

SQL Write-Ahead Overhead…

Increasing Max worker threads – A negative impact

There are many instances when Administrators come to think that increasing Max Worker Threads shall increase performance on a server with thousands of users.  This might not be always and preferable not to touch this configuration setting unless we are backed by a lot of data, research and testing.

Increasing the Max Worker threads shall directly influence the MTL sizing as the MTL is computed by the 256[default]+0.5*[Max Worker Threads] MB.  Incase the MWT is increased the actual memory that might be needed for the Buffer Pool might be lying unused in the MTL.

Also, increasing the MWT shall increase the Thread contention at the UMS schedulers and this inturn shall result in a negative impact on the performance.

For a better understanding on the UMS architecture and the influence of MWT on it, check out here and also the Books Online.

Advertisements

January 21, 2009 Posted by | SQL Server | Leave a comment

Query Timeouts – A client side feature only.

Yes thats true.. The feature of a Query timeout is a Client side feature and the Database engine doesnt have any involvement in it except accepting a “Attention event” from the Client.

Once the SQL Server database engine receives a Attention Event, it tries to stop serving to the session at the earliest but not immediately. This would take care of any locks that need to be freed before aborting the query execution. 

For a better understanding of this Event and Query Timeouts check out Ken Hendersen’s blog

January 21, 2009 Posted by | SQL Server | Leave a comment