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Hash Warning / Missing statistics

  • April 24, 2009 at 2:45 am

    #133316

    Hello,

    One customer reported client software freezes on every workstation.

    They have a dual database server synchronized by Legato. When the freeze occured, they switched to the other database instance.

    In the available trace file, before the failover, I see a lot of event "Hash Warning" followed by "Missing Column Statistics" (one every 5 minutes). After the failover, back to normal.

    Could those hash warnings cause such an heavy performance breakdown ?

    What can I do to fix those warnings ?

    Thanks

    Patrick Duflot

  • April 26, 2009 at 7:19 pm

    #984151

    According to MSDN online yeap it can. This can happen because the server doesn't have enough memory, statistics are old or don't exist.

    Have a read at http://technet.microsoft.com/en-us/library/ms190736(SQL.90).aspx.

    Check how is the server sitting with memory pressure?

    Thanks.

    Mohit.

    [font="Arial"]---

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    Microsoft FTE - SQL Server PFE

    * Some time its the search that counts, not the finding...
    * I didn't think so, but if I was wrong, I was wrong. I'd rather do something, and make a mistake than be frightened and be doing nothing. :smooooth:[/font]

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  • August 13, 2009 at 7:32 am

    #1038674

    Good Day,

    when will the number of pages/ sec be too excessive for Windows 2008 ?

  • August 13, 2009 at 7:39 am

    #1038679

    Good Day.

    I have auto create statistics activated on the database and there is a daily schedule to update the database statistics, but still the default trace displays "Hash Warning" messages . Should we rather consider to activate "auto update statistics" . Will this not cause the creation of unnecessary statistics that can impact the system again ?

  • August 13, 2009 at 1:20 pm

    #1038956

    Better turn it ON unless you see performance degradation due to update stats running on server during peak hours.

    http://blogs.msdn.com/ianjo/archive/2005/11/10/491549.aspx

    MJ

  • August 14, 2009 at 2:14 am

    #1039195

    Hi Patrick

    Can u identify the query that's causing this. Your query is using hashing and this is generally bad for performance. You will want to re-write this query in a better way. Once you are able to do this chances are that missing column statistics will be taken care of. Better concentrate on Hashing issue rather than column statistics.

    "Keep Trying"

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