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Thread: Dimension lookup - Table lock

  1. #1

    Default Dimension lookup - Table lock

    Hi everybody,

    I would like to know if components like Dimension lookup/update or Combination lookup/update lock the table during the lookup, and what kind of response may I get if any of these components tries to make the lookup over a locked table.

    The thing is that I'm in an environment on which one job is running on a server_1 and a copy of that job might be running on a server_2 (and server_3 and so on...) and I'm trying to forese any kind of issue under this configuration.

    I know that jobs cannot run clustered, but what about just having several copies of the same job running on different servers?

    Thanks,

    Mauro.

  2. #2
    Join Date
    May 2006
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    4,882

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    If Dimension lookup can't write its records it will abort.

    Running multiple copies of dimension lookup is probably not that good... what do you think happens when multiple rows on the same "entity' arrive at dimension lookup.

    Regards,
    Sven

  3. #3

    Default

    Thanks Sven,

    Ok, understood.

    Running multiple copies of dimension lookup is probably not that good... what do you think happens when multiple rows on the same "entity' arrive at dimension lookup.
    Even if I use clustering mechanism of Kettle in a single transformation?

    Thanks,

    Mauro.

  4. #4
    Join Date
    May 2006
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    Yes, even then as you will just have multiple copies running and you don't know which row will be processed in which order (for the copies), so in the unlucky case of switching executing threads you may get 2 sequential rows processed in the wrong order.

    Regards,
    Sven

  5. #5

    Default

    Thanks,

    There was one question without answer: do Dimension lookup/update and Combination lookup/update lock the underlying table during the lookup?

    Thanks Sven

  6. #6
    Join Date
    May 2006
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    Not explicitly, but e.g. in Oracle with the "right/wrong" set of constraints you will get a lock anyway. It depends.

    Regards,
    Sven

  7. #7
    Join Date
    Nov 1999
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    459

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    BTW: That's one more reason not to use constraints in a data warehouse.
    ;-) Jens

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