Creating partition tables tables that contain LOBs.

Posted on 2011-10-27
Last Modified: 2012-05-12
what is the difference between  -  PCTVERSION or RETENTION  in create table statement..?
when to use PCTVERSION and when to use  RETENTION ...?
Question by:Rao_S
    LVL 76

    Assisted Solution

    by:slightwv (䄆 Netminder)
    Have you already read what is in the docs on these?

    I've not used either of these parameters so cannot provide explicit detail into when to use one over the other.

    I've done a lot with CLOBs and have never set either one.

    Author Comment

    i was reading that document...and found it confusing, so wanted to check if somebody would explain in simple terms...
    LVL 73

    Assisted Solution

    they both have to deal with how old data in the LOBs is preserved in UNDO

    pctversion (default in manual undo) - specifies how much of the old undo to keep.

    So, if you have 50, it will keep the old data until half of your lob storage is consumed.

    retention (default in automatic undo) - specifies how much undo should be consumed to keep old data.
    LVL 73

    Accepted Solution

    to elaborate further...

    RETENTION MAX -  this means all lob changes will be maintained until you run out of UNDO

    RETENTION MIN 10 - this means enough undo storage will be used to store 10 seconds worth of changes,
     if you use this, you'll likely want a bigger number, I just picked 10 as an example.

    RETENTION AUTO  (or just RETENTION, letting it default) - this will maintain undo to support read consistency for any active transactions
      this means anybody else selecting from the table will still be able to use old versions of your data that had been accessed before changes were commited.

    RETENTION NONE - just what it sounds like,  no undo will be used. If you change the data, it's gone.

    does that help?

    Author Comment

    hi sdstuber, that is really helpful..!!! thank you very much!

    Author Closing Comment

    thank you!!!

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