Re: Re: see higher CPU usage after increase SGA
- From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 9 Jun 2004 17:03:22 +0100
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@xxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
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?
:
:
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