Lazy Writer

  • Steve Jones - SSC Editor

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    Comments posted to this topic are about the item Lazy Writer

  • Ron McCullough

    SSC Guru

    Points: 63877

    Nice clear question - thanks

    If everything seems to be going well, you have obviously overlooked something.

    Ron

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  • M&M

    SSC-Insane

    Points: 21679

    Good question, thanks.

    M&M

  • paul s-306273

    SSChampion

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    Nice question Steve.

  • Gobikannan

    SSCrazy

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    Nice question...

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    Gobikannan

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  • calvo

    SSChampion

    Points: 12930

    Wow. I really had to dig for that one.

    Pretty confusing stuff. I'd like to know if anyone here utilizes this feature of splitting physical CPUs for the purpose of creating soft-NUMA nodes for multiple lazy writer threads.

    So with one processor, do you have 1 NUMA node by default?

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  • Rafael Krisller

    Right there with Babe

    Points: 737

    Nice question! But I have questions.

    What is the best architecture in the real world? Soft-NUMA in SMP, NUMA hardware with soft-NUMA or NUMA hardware only? Is it work fine in any SQL Edition (2005/2008 - Standart, Enterprise, Workgroup, Express...)?

  • Dalton Moore

    SSC Eights!

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    Good question.

  • jcrawf02

    SSC-Insane

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    Question is missing a response: "ten forum posts" 😛

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  • Gail Shaw

    SSC Guru

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    calvo (6/10/2011)


    I'd like to know if anyone here utilizes this feature of splitting physical CPUs for the purpose of creating soft-NUMA nodes for multiple lazy writer threads.

    You get a lazy writer (and couple other things) per hard NUMA node, not soft. That reference is wrong.

    Let me see if I can find a better one....

    First the connect item for the incorrect BoL info: http://connect.microsoft.com/SQLServer/feedback/details/670328/books-online-incorrect-soft-numa-information

    And Bob Dorr's article on NUMA, this should be THE reference article on SQL and NUMA

    http://blogs.msdn.com/b/psssql/archive/2010/04/02/how-it-works-soft-numa-i-o-completion-thread-lazy-writer-workers-and-memory-nodes.aspx

    Gail Shaw
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  • mtassin

    SSC-Insane

    Points: 23096

    GilaMonster (6/10/2011)


    calvo (6/10/2011)


    I'd like to know if anyone here utilizes this feature of splitting physical CPUs for the purpose of creating soft-NUMA nodes for multiple lazy writer threads.

    You get a lazy writer (and couple other things) per hard NUMA node, not soft. That reference is wrong.

    And Bob Dorr's article on NUMA, this should be THE reference article on SQL and NUMA

    http://blogs.msdn.com/b/psssql/archive/2010/04/02/how-it-works-soft-numa-i-o-completion-thread-lazy-writer-workers-and-memory-nodes.aspx

    Except that Bob's Article says

    The benefits of soft-NUMA include reducing I/O and lazy writer bottlenecks on computers with many CPUs and no hardware NUMA. There is a single I/O thread and a single lazy writer thread for each NUMA node. Depending on the usage of the database, these single threads may be a significant performance bottleneck. Configuring four soft-NUMA nodes provides four I/O threads and four lazy writer threads, which could increase performance.



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  • calvo

    SSChampion

    Points: 12930

    mtassin, I believe Bob is quoting BOL in that paragraph.

    Gail,

    I had found that link earlier and figured BOL would be the authoratative source. Thanks for clearing that up for us.

    Bob says "The lazy writer thread creations are tied to the SQL OS view of the physical NUMA memory nodes. So whatever the hardware presents as physical NUMA nodes will equate to the number of lazy writer threads that are created."

    So no matter how many soft NUMA nodes you have, the number of lazy writer threads is based on the presence of hardware NUMAs.

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  • Rose Bud

    SSCrazy

    Points: 2963

    jcrawf02 (6/10/2011)


    Question is missing a response: "ten forum posts" 😛

    Ha, ha! Thanks for the laugh!

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