Total Server Memory vs. Target Server Memory

  • Contrary to my believe that for a good SQL Server run the two should be equal, in the last couple of days I found two articles that advice that Total Server Memory should be less then Target Server Memory< ?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

    http://download.microsoft.com/download/4/7/a/47a548b9-249e-484c-abd7-29f31282b04d/Performance_Tuning_Waits_Queues.doc

    "If Total Server Memory is well below Target Server Memory at steady state, it tells you that the server is not experiencing memory pressure."

    h71028.www7.hp.com/ERC/downloads/4AA0-2948ENW.pdf

    "Total Server Memory < 80 percent Target Server Memory "

    Is that right? If you think yes, why?

    Best Regards

     

  • SQL Server will more often than not use all of the memory available to it.  I can see on a system that is not very busy or where the requests do not require large amounts of data to be loaded up into the buffer cache that the Total Server Memory would be well below than the Target Server Memory, but I rarely see a system behave like this. 

    When the Total Server Memory and the Target Server Memory equal each other, it means that there could be signs of memory preassure and that you should consider looking at other memory related counters such as Page Life Expectancy, Buffer Cache Hit Ratio, Lazy Writes/sec, etc.

    John Rowan

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