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  1. #1
    Join Date
    Aug 2008
    Posts
    45

    Unanswered: Index compression in DB2 OS/390

    Hi all,

    I'm currently studying various kinds of compression in several databases, and I kinda confused in index compression at DB2 OS/390 version 9.5, it supposed to use a "key map" to replace dictionary, right ? But actually what happened in the process ?

    In my imagination, if there is 4 similar rows, 3 of them would be eradicated and the last one will be the key to expand the other 3 when needed, so, what does the key map do ???

  2. #2
    Join Date
    Oct 2004
    Location
    DELHI INDIA
    Posts
    338
    Are you sure INDEX can be COMPRESSED in V9.5 in OS/390? In LUW, it's not possible.

    Jayanta Datta
    DB2 UDB DBA
    IBM India, Global Delivery
    New Delhi

  3. #3
    Join Date
    Feb 2008
    Location
    Japan
    Posts
    3,483
    I searched IBM Redbooks
    http://www.redbooks.ibm.com/
    with keywords '"DB2 9" AND z/OS', then I got some interesting documents.

    14 results in Redbooks, Redpapers, Drafts and Technotes
    http://www.redbooks.ibm.com/cgi-bin/searchsite.cgi?query="DB2+9"+AND+z/OS

    , especcialy I was interested in
    Index Compression with DB2 9 for z/OS
    http://www.redbooks.ibm.com/abstract...4345.html?Open

  4. #4
    Join Date
    Sep 2004
    Location
    Belgium
    Posts
    1,126
    Quote Originally Posted by JAYANTA_DATTA
    Are you sure INDEX can be COMPRESSED in V9.5 in OS/390? In LUW, it's not possible.
    Yes, it can. Actually, compression is only applied to the leaf pages, and it uses a fixed algorithm, i.e., one that does not depend on a compression dictionary. (Or stated otherwise, it depends on a single, fixed, built-in dictionary.)
    After compression, the leaf pages must have been reduced to (less than) 4K, which was the (uncompressed) index page size limit in older versions of DB2 for z/OS. Through compression, the actual, uncompressed size of the leaf pages can now be 8K, 16K or 32K.
    --_Peter Vanroose,
    __IBM Certified Database Administrator, DB2 9 for z/OS
    __IBM Certified Application Developer
    __ABIS Training and Consulting
    __http://www.abis.be/

  5. #5
    Join Date
    Oct 2004
    Location
    DELHI INDIA
    Posts
    338
    Thanks Peter. Never worked on DB2 Z/OS, but great to know that stuff about Index-Compression.

    Jayanta Datta
    DB2 UDB DBA
    IBM India, Global Delivery
    New Delhi

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