RE: Is DBFMRC limited to 16 on AIX ?

From: Bobak, Mark <>
Date: Mon, 4 Aug 2008 11:24:44 -0400
Message-ID: <>


I'm not an AIX guy, but, what's your db_block_size? If it's 8k, that means w/ dbfmrc=16, you're doing 128k reads.

Is there some reason AIX is limited to 128k reads?

I know the limit on Solaris and Linux is 1M.


From: [] On Behalf Of Hemant K Chitale [] Sent: Monday, August 04, 2008 10:51 AM
Subject: Is DBFMRC limited to 16 on AIX ?

Testing db_file_multiblock_read_count at 128 on AIX we found much poorer performance (higher read times of 35ms) then that for dbfmrc at 16 (3ms).

One of the team (not from Oracle) referred us to this section (A.2.5) of the Oracle Database Administrator's Reference for Unix
"Setting a large value for the DB_FILE_MULTIBLOCK_READ_COUNT
initialization parameter usually yields better I/O throughput on sequential scans. On AIX, this parameter ranges from 1 to 512, but using a value higher than 16 usually does not provide additional performance gain.".
How did Oracle come up with this limit of 16 for AIX ? Is it only for for DIO / CIO or NOT for DIO / CIO ?

What experiences do Oracle on AIX administrators have with dbfmrc ?

Hemant K Chitale

"A 'No' uttered from the deepest conviction is better than a 'Yes'
merely uttered to please, or worse, to avoid trouble." Mohandas Gandhi Quotes


Received on Mon Aug 04 2008 - 10:24:44 CDT

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