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(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
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Title: Message
- consistent read gets Sultan Syed
- Re: consistent read gets Bobak, Mark
- Re: consistent read gets Sultan Syed
