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 [EMAIL PROTECTED]
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
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|Author: Hillman, Alex
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