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Compressed dimension values on MDC - IBM DB2

Hello, I've attended a few seminars on DB2 V8 Multi-Dimensional Clustering, and I'm trying to remember some details about a rumour I remember hearing about compression. Given that the dimension values must be identical for all rows in a given MDC block, does IBM plan to alter the structure of the MDC rows to avoid the redundant storage of the dimension values? The space savings could be significant if the dimension values were only stored once per block instead of within every row. Thanks, Fred...

  1. #1

    Default Compressed dimension values on MDC

    Hello,

    I've attended a few seminars on DB2 V8 Multi-Dimensional Clustering,
    and I'm trying to remember some details about a rumour I remember
    hearing about compression. Given that the dimension values must be
    identical for all rows in a given MDC block, does IBM plan to alter
    the structure of the MDC rows to avoid the redundant storage of the
    dimension values? The space savings could be significant if the
    dimension values were only stored once per block instead of within
    every row.

    Thanks,
    Fred
    Fred Guest

  2. #2

    Default Re: Compressed dimension values on MDC



    Fred wrote:
    > Hello,
    >
    > I've attended a few seminars on DB2 V8 Multi-Dimensional Clustering,
    > and I'm trying to remember some details about a rumour I remember
    > hearing about compression.
    Don't know why this is a rumour?
    > Given that the dimension values must be
    > identical for all rows in a given MDC block, does IBM plan to alter
    > the structure of the MDC rows to avoid the redundant storage of the
    > dimension values? The space savings could be significant if the
    > dimension values were only stored once per block instead of within
    > every row.
    I agree. I think IBM should consider to compress the MDC table or
    blocks. Yes the compression/decompression will cost additional CPU
    workload. But this also means less I/O read, less bufferpool space to
    hold the blocks/pages, ...

    >
    >
    > Thanks,
    > Fred
    Fan Ruo Xin Guest

  3. #3

    Default Re: Compressed dimension values on MDC

    MDC compression of dimension values is certainly a recognized feature that
    we will be evaluating for the future. As Fred correctly points out, every
    record in a block in an MDC table has the same values for all columns
    involved in the dimensions defined on that table, so there is space savings
    to be had by storing the dimension values on a per-block vs a per-record
    basis. However, note that in order to retrieve the dimension values for a
    particular record, we may have to access 2 pages in the block if the record
    is on a different page than that where the dimension values are stored. This
    would present additional overhead, as well as could cause contention for the
    page containing the dimension values. Thus, for concurrency and performance,
    we would likely store the dimension values once per page instead of once per
    block.

    Best regards

    Leslie

    "Fan Ruo Xin" <fanruoxsbcglobal.net> wrote in message
    news:3F66760A.CCB80203sbcglobal.net...
    >
    >
    > Fred wrote:
    >
    > > Hello,
    > >
    > > I've attended a few seminars on DB2 V8 Multi-Dimensional Clustering,
    > > and I'm trying to remember some details about a rumour I remember
    > > hearing about compression.
    >
    > Don't know why this is a rumour?
    >
    > > Given that the dimension values must be
    > > identical for all rows in a given MDC block, does IBM plan to alter
    > > the structure of the MDC rows to avoid the redundant storage of the
    > > dimension values? The space savings could be significant if the
    > > dimension values were only stored once per block instead of within
    > > every row.
    >
    > I agree. I think IBM should consider to compress the MDC table or
    > blocks. Yes the compression/decompression will cost additional CPU
    > workload. But this also means less I/O read, less bufferpool space to
    > hold the blocks/pages, ...
    >
    >
    > >
    > >
    > > Thanks,
    > > Fred
    >

    Leslie Cranston Guest

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