Message
(I'm
sending the reply to the freelists.org list as well. Hope you all agree
that's a reasonable thing to do.)
no work - consistent read
gets - Oracle needs a block that's consistent w/
a particular SCN, goes to the buffer cache, finds it there. It's
done.
cleanouts only - consistent read gets - Oracle needs a block that's consistent w/ a
particular SCN, goes to the buffer cache, finds it there, but discovers it was
recently modified and never cleaned out. It needs to do extra work to
clean out the block.
rollbacks only - consistent read gets - Oracle needs a block that's consistent w/ a
particular SCN, goes to the buffer cache, finds it there, but discovers that the
SCN on the block is too recent. So, it refers to data stored in rollback,
to roll back the block until it's old enough to be consistent w/ the query
SCN.
cleanouts and rollbacks - consistent read gets - Oracle needs a block that's consistent w/ a
particular SCN, but discovers it needs to cleanout the block, does so, then
discovers it needs to roll it back, and does that
too.
Hope that's clear. In reality, there are lots of
different types of situations that can occur. The above is probably a bit
simplified, but I think accurate as far as it
goes.
-Mark
Mark J.
Bobak
Oracle DBA
ProQuest Company
Ann Arbor,
MI
"Imagination
was given to man to compensate him for what he is not, and a sense of humor was
provided to console him for what he is." --Unknown
Hi all,
Could somebody give example scenario for the
followings please
no work - consistent read
gets
cleanouts only - consistent read
gets
rollbacks only - consistent read
gets
cleanouts and rollbacks - consistent read gets
And
Is ther difference between consistent read gets
and consistent gets?
Thanks in advance
Syed
--
Please see the official ORACLE-L FAQ: http://www.orafaq.net
--
Author: Bobak, Mark
INET: Mark.Bobak_at_il.proquest.com
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Received on Mon Jan 26 2004 - 08:39:28 CST
