RE: how do you decide your db_cache_size

  • From: "Gogala, Mladen" <MGogala@xxxxxxxxxxxxxxxxxxxx>
  • To: "'ganstadba@xxxxxxxxxxx'" <ganstadba@xxxxxxxxxxx>, oracle-l@xxxxxxxxxxxxx
  • Date: Wed, 14 Sep 2005 14:21:29 -0400

Well, the initial sizing is the matter of opinion. I usually start with 256M
and then increase until waits on free buffers go away or until the end users
are satisfied with the performance, whichever happens first. It's the end
luser that is driving the tuning process, not the DBA. I also subscribe to 
the binary religion: I somehow believe (from the days of mVaxII) that binary
numbers are easier for the CPU to operate on and that using binary numbers
will help me secure the afterlife and not re-incarnate as a MS-Windows

Mladen Gogala
Ext. 121

-----Original Message-----
From: Michael McMullen [mailto:ganstadba@xxxxxxxxxxx] 
Sent: Wednesday, September 14, 2005 12:20 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: how do you decide your db_cache_size

In reference to Buffer Cache hit very low I should have said keep the SGA
below 2GB but I'm standing by enlarging the buffer cache. I never said it
would help the BCHR. I'm a firm believer in method R and I don't live in
Kittrell NC but to exaggerate to make a point what if your buffer cache is
1Mb? Do you still say figure out your bad sql? No, you increase it, then
work on the bad sql. Personally, I think an 250Mb  cache size for a 40Gb
database doing large batch jobs is too small and really the db_cache_size
would be lower as I think that was referring to total SGA.

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