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Showing page 2 of 4 (36 total posts)
  • Performance Impact: file fragmentation and SAN – Part III

    256KB Sequential Reads   In my two previous posts (1, 2), I highlighted the fact that while file fragmentation had a huge adverse performance impact on directly attached storage (DAS), it did not have much, if any, impact on the drive presented from a high end enterprise class disk array. That observation was derived from running disk I/O ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on December 10, 2008
  • Large Query Performance and Query Parallelism

    [2008/08/25] This post has been modified significantly to correct some inaccurate statements because I mis-read Joe Chang's post. Joe Chang posted some interesting results using the TPC-H queries with the scale factor set to 10. I happened to have done something similar, and naturally noticed a rather significant difference between his results ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on August 24, 2008
  • Performance impact of controller cache: SQL Server read only workloads

    In my previous post, I looked at how a typical OLTP workload may be affected by various controller cache configurations. And the conclusion was that giving too much cache (say all 512MB) to reads hurt the OLTP performance. The primary reason was that the writes from the OLTP workloads were starved of cache. Now, let's take a look at how the ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on March 31, 2008
  • Performance impact of controller cache: SQL Server large operations

    In my previous post on the performance impact of controller cache configurations, I presented some empirical results showing the performance impact of configuring the controller cache to various read/write settings on large sequential I/Os.   Why did I single out large sequential I/Os? That's because large sequential I/Os are heavily used ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on March 26, 2008
  • Performance impact of controller read cache: large sequential I/Os

    In the next several blog posts, I’ll share with you some empirical results concerning the performance impact of configuring the read/write cache of a disk controller.   In the comments on Joe Chang’s blog at this site on Storage Performance for SQL Server, some statements were made concerning the performance impact of read cache in a disk ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on March 24, 2008
  • Performance Impact: Setting a Database to Read Only

    It is widely quoted that if a SQL Server database is set to Read Only (using ALTER DATABASE ... SET READ_ONLY), your queries may run faster because no locking occurs in a read-only database. This all makes sense conceptually. But I have not seen any empirical data to get a feel for the extent of the impact. And it's always good to have some solid ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on October 1, 2007
  • Performance Impact: Manual Checkpoints are not Necessarily Evil

    In my two previous posts on the performance impact of frequent manual checkpoints and the I/O behavior of frequent manual checkpoints, I demonstrated that frequently issuing manual checkpoints can be bad for performance and why it's bad from the storage perspective. If you were led to believe that manual checkpoints were always bad, that wasn't ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on August 20, 2007
  • Performance Impact: Frequent Manual Checkpoints and Their I/O Behavior

    In my previous blog post on the performance impact of frequent manual checkpoints, I highlighted the performance peril of going overboard with manual checkpoints, and I suggested that a major contributing factor was the failure of frequent manual checkpoints to take advantage of the throughput potential of the underlying storage. But I didn't ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on August 17, 2007
  • Performance Impact: Frequent Manual Checkpoints

    Recently, I was asked why the following script took a very long time to insert 24GB of data into a single table in SQL Server 2005 (the database was in the simple recovery mode): -- Name: Script 1SET NOCOUNT ON SET IMPLICIT_TRANSACTIONS ON DECLARE @i int SET @i = 1 WHILE @i <= 3145728 -- (1024*1024*3) BEGIN INSERT tbTest(i, ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on August 13, 2007
  • Reduce the Contention on tempdb with Trace Flag 1118: Take 2

    My earlier attempt to see what's going on with trace flag 1118 on SQL Server 2005 SP2 (9.00.3042) didn't take me too far because the results were not conclusive. I was motivated by seemingly conflicting suggestions from KB article Q936185 and whitepaper Working with tempdb in SQL Server 2005. The KB article lists the following as conditions that ...
    Posted to Linchi Shea (Weblog) by Linchi Shea on August 10, 2007
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