FAQ
In Steve Adams sample of performance report there is a suggestion to use
trigger after row update instead of before row update because it will halve
the number of redo records created for row locks. Anybody has diferent
opinion?

Alex Hillman
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  • Jonathan Lewis at Aug 18, 2001 at 10:00 am
    I think Steve is probably a little more precise
    in his statement. But there are definitely cases
    where using before-row triggers is more expensive
    that using after-row triggers to do the same job.
    The cost appears as extra current mode gets
    and redo log generation.

    Thomas Kyte has a demonstration of this in
    his book "Expert One on One: Oracle"

    However, you do need to consider carefully
    what your triggers are trying to do. For example,
    (extreme case for the purposes of making a point)
    if the trigger is supposed to cause a failure in
    a larger percentage of cases then it is better
    to do:

    before row trigger - fail
    than

    update row
    after row trigger - fail
    roll back update

    General principle, therefore (which may be subject
    to change in future versions of Oracle). All other things
    being equal, an after row trigger is probably cheaper
    than a before-row; but there are inevitably cases where
    it doesn't really matter, and special cases where it is
    not true.

    Jonathan Lewis

    Host to The Co-operative Oracle Users' FAQ
    http://www.jlcomp.demon.co.uk/faq/ind_faq.html

    Author of:
    Practical Oracle 8i: Building Efficient Databases
    See http://www.jlcomp.demon.co.uk/book_rev.html

    For latest news of public appearances
    See http://www.jlcomp.demon.co.uk

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    -----Original Message-----
    To: Multiple recipients of list ORACLE-L
    Date: 17 August 2001 23:16
    In Steve Adams sample of performance report there is a suggestion to use
    trigger after row update instead of before row update because it
    will halve
    the number of redo records created for row locks. Anybody has diferent
    opinion?

    Alex Hillman
    --
    Please see the official ORACLE-L FAQ: http://www.orafaq.com
    --
    Author: Hillman, Alex
    INET: Alex.Hillman_at_usmint.treas.gov

    Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
    San Diego, California -- Public Internet access / Mailing Lists
    --------------------------------------------------------------------
    To REMOVE yourself from this mailing list, send an E-Mail message
    to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
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    (or the name of mailing list you want to be removed from). You may
    also send the HELP command for other information (like subscribing).
    --
    Please see the official ORACLE-L FAQ: http://www.orafaq.com
    --
    Author: Jonathan Lewis
    INET: jonathan_at_jlcomp.demon.co.uk

    Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
    San Diego, California -- Public Internet access / Mailing Lists
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postedAug 17, '01 at 9:49p
activeAug 18, '01 at 10:00a
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Jonathan Lewis: 1 post Hillman, Alex: 1 post

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