RE: DB Block Buffers - Too Much ???

From: Weaver, Walt <wweaver_at_rightnowtech.com>
Date: Wed, 21 Jun 2000 11:05:52 -0600
Message-Id: <10535.110028@fatcity.com>

Just out of curiousity, did you measure hit ratio soon after re-starting the database? Wouldn't the hit ratio be misleadingly low for a while, since Oracle was probably busy reading disk and loading stuff into the buffers?

Other than that, I suppose you could monitor vmstat or some other utility to see if excessive memory swapping is going on.

--Walt Weaver

Bozeman, Montana, USA

-----Original Message-----

From: Deepak Sharma [mailto:sharmakdeep_at_yahoo.com] Sent: Wednesday, June 21, 2000 11:26 AM
To: Multiple recipients of list ORACLE-L Subject: DB Block Buffers - Too Much ???

Recently on one of our test systems the Buffer Cache Hit Ratio was showing 80%. I increased
db_block_buffers from 6000 to 16000, and the after that the hit ratio has dropped to 55%. It seemed strange to me that increasing db_block_buffers should actually decrease performance, until I read Oracle tuning tips from Richard Niemiec, where he mentions too much db_block_buffers is not good too, as it may lead to swapping. My question is how do you determine whether the buffers are too low or too high ?

SQL> select state, count(*) from x$bh group by state;

STATE COUNT(*)
---------- ----------

         1      13047
         3       2953

Does state = '1' mean this memory is not being used and if so, should I decrease the buffers ?

Deepak

Oracle DBA,
Minneapolis, MN
USA

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Author: Deepak Sharma
INET: sharmakdeep_at_yahoo.com

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