Wouldnt this indicate hot blocks? How do I deduce from this, I have a large
value for "db_block_buffers"?
Thanks
Raj
"Jonathan Lewis"
<[EMAIL PROTECTED] To: Multiple recipients of list
ORACLE-L <[EMAIL PROTECTED]>
mon.co.uk> cc:
Sent by: Subject: Re: Slow database, too
MANY buffers???
[EMAIL PROTECTED]
January 23, 2003
02:49 PM
Please respond to
ORACLE-L
You could try:
select file#, dbablk, count(*)
from x$bh
group by
file#, dbablk
having count(*) > 5
;
(technically you should include the
tablespace number, but that won't
matter if you have less than 1022
files).
This will report the blocks which have an
unusually large number of CR copies in the
buffer. There is a nominal limit of 7, but
if your buffer is excessive for the work done
then there is a fair chance that the most
intensively used blocks will have far more
buffers. (The worst case I saw was something
like 75).
The side effects of this would include lots of
spinning and sleeping on the cache buffers
chains latch.
Regards
Jonathan Lewis
http://www.jlcomp.demon.co.uk
Coming soon a new one-day tutorial:
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(see http://www.jlcomp.demon.co.uk/tutorial.html )
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-----Original Message-----
To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>
Date: 23 January 2003 19:05
I've got a cust that is showing some signs that one would
think is having a horrible problem on I/O...
I suspect it is the "error" of having a **HUGE** value
in db_block_buffers and it's constantly crunching memory
trying to figure out which ones to free up. It's only
256 meg, but depending on load, it may be too much. SGA
is 687 meg.
While I've got hundreds of SQL, I'm not sure I have one
to diagnose buffer utilization. It's also version 8.1.7
and I could probably do some tweaking of buffers.
It's Oracle CRM with a lot of customization and I'm also
finding some SQL that's getting a bit ugly under there.
Maks.
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