AIX and Largefiles Performance
- From: Byron Pearce <pearceb@xxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Fri, 25 Jun 2004 15:50:42 -0500
All:
I am not a native of Planet IBM, but this morning one of the systems
administrators here forwarded over a tuning guide from the mother ship
regarding Oracle on AIX. There were a number of interesting things in
there that I am still working through, but one particular item piqued my
interest.
"... Do not allocate a JFS with the large file enabled (bf) attribute.
The big file attribute increases the minimum DIO transfer size
(diocapbuf.dio_min returned by the finfo system call) from 4K to 128K,
forcing Oracle to read and write a minimum of 128K byte to exploit DIO.
Please note that 2GB is the largest file size applications (including
Oracle) can use in a JFS without the 'bf' attribute -- large file
enablement. Do not allocate a compressed JFS, which defeats DIO.
Respecting the JFS 2GB maximum file size avoids potential file level
inode locking performance issues in JFS or JFS2 (without CIO), but a
downside of small (2GB) files in a very large database (VLDB)
environment is the time required to open/close files during the
startup/shutdown."
I have worked on most of the other major O/S variants, and this is the
first time I have ever heard the largefiles settings have a negative
impact on performance. In the interest of scientific investigation on
this topic, I am officially checking my ego at the door and opening my
mind to this possibility. I am trying to do some research on this, but,
thus far, my findings have been sparse.
Has anyone heard this before? Or is this a performance myth along the
lines of the BCHR's (if so it is a first for me to hear it)? Or is
there a genuine benefit to be gained by doing this?
Any comments or thoughts on this matter would be appreciated.
--
====================================================================
Byron Pearce mailto:pearceb@xxxxxxxxxx
Tenure Systems, Inc. Dallas/Fort Worth, TX
"It's hard to be a ninja when you wear a beeper."
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