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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Buffer use under Oracle
I didn't get the sense from the original note that there was a 'free buffer
waits' problem, so I'm assuming that there's not really demand for new
buffers. I thought the original post was an expression of curiosity about
how there could be so many index blocks in the buffer cache at the same
time. (Perhaps I didn't read carefully enough, and it's of course difficult
to tell at this point what the original post said because the original post
isn't present in this thread anymore.)
I'm curious though, if a cloned buffer is accessed frequently by running queries, are you saying that the probability is high that it will get aged out prematurely, and therefore force re-reconstruction the next time that particular incarnation of the buffer is required?
Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
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-----Original Message-----
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org]
On Behalf Of K Gopalakrishnan
Sent: Wednesday, May 12, 2004 10:47 AM
To: oracle-l_at_freelists.org
Subject: Re: Buffer use under Oracle
Cary:
I don't think this is right unless I am reading between lines ;). Cloned buffers are always kept in the cold end in the new alogorithm and they are ready to be flushed when ever there is a demand for new buffers. The CR buffers are kept in the FROZEN end (note the word freeze in the parameter, it is not cold. Freeze)
Of course the behavior can be controlled by _db_aging_freeze_cr parameter.
KG
> >Why aren't the old ones freed when a new one is created?
>
> ...because of Oracle's LRU buffer cache management algorithm.
> Currently-executing queries may "like" having a slightly older CR copy =
> of a
> newly modified block in the buffer cache. Such a block will tend to =
> remain
> cached as long as some session keeps using it. Those blocks are in your
> buffer cache because your application needs them.
>
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