Sladescross's Blog

Blogging about Sharepoint related stuff

SQL Peformance Urban Legends June 16, 2010

Filed under: SQL Performance,TempDb — sladescross @ 7:11 pm

Tempdb is the database with the highest level of create and drop actions and under high stress the allocation pages, syscolumns and sysobjects can become bottlenecks.   SQL Server 2005 reduces contention with the ‘cached temp table’ feature and allocation contention skip ahead actions.

When multiple workers are attempting to create or drop objects in tempdb you can decrease the bottleneck by having

  • As many files in tempdb as schedulers
  • All files sizes are equal
  • Uniform allocations enabled (-T1118)

The key for SQL Server is the I/O response times.  Start by looking at the Average Disk Seconds Per Transfer for the same I/O path.  Then look at the SQL Server sysprocesses and waitstats for buffer based I/O wait information.   You want to see evidence from SQL Server that the disk queue length is related to an I/O bottleneck.

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