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Thread: Merge Scans

  1. #1
    Join Date
    May 2002
    Posts
    30

    Unanswered: Merge Scans

    I get loads of merge scans in my access plans ... This causes sorts leading to slow response and excessive CPU Utilization

    Are there any generic tips/techniques to avoid Merge Scans ?

    BTW, this is DB2 V8 on AIX

    Thanks

  2. #2
    Join Date
    Jan 2004
    Location
    Europe, Finland, Helsinki
    Posts
    64
    Well...my knowledge is from z/OS environment, but priciples are usually same.

    Probably some of these are helpfull:
    - your tables may be large and have no (good) indexes with matching columns.
    - join predicate are not restictive enough and offers too little filtering (many-to-many join?)
    - RUNSTATS ok? DB2 is thinking that both outer and inner table will produce a lot of rows - so MERGE SCAN is chosen.

    Cheers, Bill

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