RE: how do you decide your db_cache_size

  • From: "Allen, Brandon" <Brandon.Allen@xxxxxxxxxxx>
  • To: <MGogala@xxxxxxxxxxxxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
  • Date: Wed, 14 Sep 2005 11:27:51 -0700

I'm with you Mladen - I can't stand it when someone creates a "1GB" datafile 
with a size of 1000MB.  Infidels!  :-)

-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]On 
Behalf Of Gogala, Mladen
Sent: Wednesday, September 14, 2005 11:21 AM
To: 'ganstadba@xxxxxxxxxxx'; oracle-l@xxxxxxxxxxxxx
Subject: RE: how do you decide your db_cache_size



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 workstation.

-- 
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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