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Thread: Pctfree/pctused

  1. #1
    Join Date
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    Pctfree/pctused

    Please advise.
    Daily data is refreshed in 100 tables.Some of the rows have Avg row length between 1025 –1150 bytes I have to recreate the tables/indexes
    No updates against the tables, only:
    1.truncate
    2.inserts
    What experienced DBA’s would set for pctfree /pctused

    Please help.
    Thanks

  2. #2
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    PCTFREE is the space reserved for updates.
    PCTUSED is threshhold for putting a data block onto the freelist. That is, when the free space/total space percentage is less than PCTUSED, the data block goes back on the freelist.

    If you perform no updates, then you should set your PCTFREE to be very low, i.e. 5 or 10.

    If you are deleting all of the data, you can set the PCTUSED to be low also, say 25 or 30. It seems irrelevant though if all the data is deleted.
    David Knight
    OCP DBA 8i, 9i, 10g

  3. #3
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    I don't see the need to stop a PCTFREE=5 or 10 -- set PCTFREE=0 and use the whole block.
    David Aldridge,
    "The Oracle Sponge"

    Senior Manager, Business Intelligence Development
    XM Satellite Radio
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    Oracle ACE

  4. #4
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    slimdave,

    dknight is correct because pctfree does not refer just to updates. It also refers to transactions ocurring in a data block. So, each transaction ocurring with a row means the block needs free space for this overhead allocation, then pctfree space will be used, so pctfree should be more than 0.

    F

  5. #5
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    What kind of transactions do youmean, and what is it that they need the free space for?
    David Aldridge,
    "The Oracle Sponge"

    Senior Manager, Business Intelligence Development
    XM Satellite Radio
    Washington, DC

    Oracle ACE

  6. #6
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    Oh that kind of transaction entry, sorry, it's a bit late for brain work.

    That's only for insert, delete, update and "select for update", none of which are going to be going on in this case (insert and truncate). And you only need about 23 bytes for those, which is much less than half-a-percent of an 8k block, so even if you were looking a having to guarantee space for the transaction entries, you could do so with a pctfree of 1.

    In this case I'd still go for pctfree=0
    David Aldridge,
    "The Oracle Sponge"

    Senior Manager, Business Intelligence Development
    XM Satellite Radio
    Washington, DC

    Oracle ACE

  7. #7
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    I thought that space is reserved in the block overhead and not pctfree?

  8. #8
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    Originally posted by pando
    I thought that space is reserved in the block overhead and not pctfree?
    Check http://www.dbasupport.com/forums/sho...threadid=22877 for the explanation.
    Jurij Modic
    ASCII a stupid question, get a stupid ANSI
    24 hours in a day .... 24 beer in a case .... coincidence?

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