Re: CBC Latch contention in 10g

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Thu, 21 Oct 2004 17:38:16 +0100
Message-ID: <004901c4b78c$5f90b500$6702a8c0@Primary>

I don't know if there is any published material on this - I think I got the important bit of it from Steve Adams' masterclass.

It's likely that the sharable cache latch used some of the time is better than never having it at all - and Oracle does keep finding new ways to (a) reduce the latch acquisition, and (b) switch to single latch reads anyway, so scalability does keep improving.

Where did you see a fanfare about sharable latches, I didn't spot it. I'd be interested to see how it was presented.

Regards

Jonathan Lewis

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

http://www.jlcomp.demon.co.uk/seminar.html Optimising Oracle Seminar - schedule updated Sept 19th

• Original Message ----- From: "Smiley John - IL" <SMILEYJ_at_tusc.com> To: "'Jonathan Lewis'" <jonathan_at_jlcomp.demon.co.uk> Cc: <oracle-l_at_freelists.org> Sent: Thursday, October 21, 2004 3:57 PM Subject: RE: CBC Latch contention in 10g

: Thanks Jonathan. You've given me something to think about. It had not
: occurred to me that the buffer header would have to be modified in order
: inspect the buffer for consistent read purposes and that the CBC latch
would
: not be taken in a sharable mode. This puts some rather severe limitations
: on CBC latch sharing and makes me wonder why Oracle bothered to implement
: it. It would also seem to place some severe limits on scalability even in
: read-only environments. CBC latch sharing was announced with some
fanfare,
: so I had expected it to be of more consequence.

:

: I would like to understand this better. Any references you can provide
: would be appreciated. I've read most of the easily obtainable literature:
: Cary's Optimizing Oracle Performance, both of Tom Kyte's outstanding
books,
: Richmond Shee's Oracle Wait Interface book, Steve Adam's Internals book,
and
: your Practical Oracle 8i book to name a few. However, none of these
delved
: deep enough into what exactly happens during a buffer get for me to latch
: onto the fact (pun intended) that the buffer header has to be modified if
: all I want to do is read the buffer. In general, there's a lot more going
: on under the covers that none of the published resources I've come across
so
: far seem to address.

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Received on Thu Oct 21 2004 - 11:33:50 CDT