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Thread: Prefetch Issue

  1. #1
    Join Date
    Apr 2004
    Posts
    190

    Unanswered: Prefetch Issue

    DB21085I Instance "db2inst1" uses "64" bits and DB2 code release "SQL08028"
    with level identifier "03090106".
    Informational tokens are "DB2 v8.1.0.136", "s070720", "U810953", and FixPak
    "15".
    Product is installed at "/opt/IBM/db2/V8.1".

    Solaris 8

    I have a query similiar to:

    (1) select col1, col2 from tableA where date between x and y
    and col3 in (subselectA)
    and col4 in (subselectB)
    group by col1

    (2) select col1, col2 from tableA where date between x and y
    and col3 in (subselectA)
    group by col1

    (3) select col1, col2 from tableA where date between x and y
    group by col1

    1 Does not use prefetching for tableA, however both 2 and 3 does. Any ideas why ?

  2. #2
    Join Date
    Aug 2001
    Location
    UK
    Posts
    4,650
    I guess , as per statistics, "col4 in (subselectB)" will reduce the resultset to a small number.
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