Re: Re: see higher CPU usage after increase SGA

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Wed, 9 Jun 2004 17:03:22 +0100
Message-ID: <025201c44e3b$4c2003a0$7102a8c0@Primary>

Buffer get -

    Oracle has to acquire the cache buffers chains latch     Scan a buffer chain
    Generate a pin for a buffer header
    Release the latch
    Use the buffer
    Acquire the latch
    Detach and release the pin
    Drop the latch

Buffer is pinned count: -

Oracle has previously pinned a buffer, and not released it immediately. A pin may be held for the duration of a database call. Oracle can revisit the buffer by traversing the pin without acquiring the latch, because the presence of the pin ensures that no other session could have acquired that buffer in a conflicting fashion.

I recall an example from a couple of years ago when Mark Bobak reported 10,000 gets apparently taking a couple of CPU minutes. In fact there were also a few million 'buffer is pinned' to be accounted for as well.

Regards

Jonathan Lewis

http://www.jlcomp.demon.co.uk

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 May 1st

Original Message ----- From: <ryan.gaffuri_at_cox.net> To: <oracle-l_at_freelists.org> Sent: Wednesday, June 09, 2004 4:50 PM Subject: Re: Re: see higher CPU usage after increase SGA

: what is the difference between a buffer get and a buffer is pinned count?
:
:

Please see the official ORACLE-L FAQ: http://www.orafaq.com

To unsubscribe send email to: oracle-l-request_at_freelists.org put 'unsubscribe' in the subject line.

--
Archives are at http://www.freelists.org/archives/oracle-l/
FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html
-----------------------------------------------------------------

Received on Wed Jun 09 2004 - 11:00:19 CDT