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Thread: rebalancing

  1. #1
    Join Date
    Feb 2005

    Unanswered: rebalancing

    Hi All,

    Can somebody explain to be the concept of rebalancing (DB2 for LUW). It sounds like redistributing data across the available containers.
    For example:
    Let's say
    I have a DMS TS S1, using container file F1.
    F1 is 600 MB (as per disk utilization)
    I add two more containers F2 AND F3 (same size as F1)
    based on my interpretation of the term rebalancing, after rebalancing, I expect to see the usage as
    file F1 is 200MB
    file F2 is 200MB
    file F3 is 200MB
    However, I don't see what I thought I might see.
    Could someone please explain this concept of rebalancing to me ? Is this something specific to the LUW world, or does it also exist in the z/OS world ?


  2. #2
    Join Date
    Aug 2001
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  3. #3
    Join Date
    Apr 2006
    when you add containers F2 ,F3 (600M) to TS S1, OS will alloc file ,its sizewill be 600M as you see.
    rebalance means DB2 will move Extents from f1 to f2,f3,in order to improve IO performance. F1 may be not fully used before rebalance,for example , it is only used 300M,other 300M space is empty. After rebalance , F1 will be used 100M by DB2,other 500M space is not used. F2,F3 too.
    But when we see F1,F2,F3 from OS, it still is 600M.

  4. #4
    Join Date
    Jun 2003

    Rebalance takesplace...

    The information is documented
    in the infocenter at:
    In that page search for "rebalancing"

    Check the document "How containers are added and extended in DMS table

    It tells the following:

    "if you have a number of containers that are the same size, and you ex
    tend each of them by the same amount, the relative positions of the
    extents will not change, and a rebalance will occur."

    Therefore, instead of adding 50000 to one container, if you added
    12500 pages each in all 4 containers when all the containers were of
    same size, then rebalance would not occurr.

    The actual issue is if an extent needs to move from one strip set to
    another, then rebalance occurrs.

  5. #5
    Join Date
    Aug 2002
    Chennai, India
    You could also avoid rebalancing, by use of BEGIN STRIP SET option of the ALTER command when you add a container to the DMS table space.


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