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  1. #1
    Join Date
    Oct 2007

    Unanswered: How to calculate the Numblockpages


    Informational tokens are "DB2 v9.7.0.5",

    i need to set a numblockpages for bufferpool which is having low hit ratio and also page stealing

    NPAGES -- 4048
    PAGESIZE -- 4096

    NUMBLOCKPAGES should be 2-3 % of bufferpool size

    this are the comments
    Note that the parameter name is slightly misleading in that it is not the number of pages that are allocated to the block-based area, but the number of extents. The actual number of pages allocated is (NUMBLOCKPAGES * EXTENTSIZE). Additionally, although there is a restriction that NUMBLOCKPAGES cannot be more than 98% of the overall buffer pool size.

    4048 = 3 % = 121

    extentsize = 32

    121 * 32 = 3872 pages , the numblockpages should be 3872 pages ??


  2. #2
    Join Date
    Jul 2013
    Moscow, Russia
    Provided Answers: 55

    I think this size calculation formula (NUMBLOCKPAGES * EXTENTSIZE) is not correct. There is no such a bufferpool parameter as EXTENTSIZE.
    Multiple tablespaces with different extent sizes can be bound to this bufferpool, so it's hard to believe that the bufferpool size depends on some of the extent sizes of the tablespaces bound to this bufferpool. Documentation states that NUMBLOCKPAGES is namely number of pages and not extents as well.
    Seems that you got it from the DB2 for LUW Performance: Buffer Pool Tuning blog post, and I think that the author was not correct here.

  3. #3
    Join Date
    Oct 2007
    hi Mark,

    Thanks for the reply, yes i was referring that link for bufferpool tunning,

    Actually we have 2 bp which hit ratio is constantly low below 50 % and even, block_ios is 0 and vectored io is more

    was googling about increase the hit ratio, and its pages assign is also let, 4048 * 8192, its shared system, there are 5 instance sharing this server,

    This db is having other BP also in it which BP hit ratio is good.

    altering numblocksize to 5 % of bufferpool pages, will it shld give imrpovorment.


  4. #4
    Join Date
    Jun 2003
    Toronto, Canada
    Provided Answers: 1
    Allocating a block area is not likely to improve your bufferpool efficiency. It may improve your prefetch performance, but we (and probably you) don't know if it is even a problem in your environment. I'd probably start with simply increasing your existing bufferpool to at least twice its current size, because 4K pages is way too little.
    "It does not work" is not a valid problem statement.

  5. #5
    Join Date
    May 2012
    Canberra, Australia
    Provided Answers: 6
    How much memory do you have on this server and how many dbs per instance? Are they in auto memory mgmt mode or all in manual?

    "All parts should go together without forcing. You must remember that the parts you are reassembling were disassembled by you. Therefore, if you can’t get them together again, there must be a reason. By all means, do not use hammer.” — IBM maintenance manual, 1975 "

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