Re: Re: see higher CPU usage after increase SGA

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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