Setting the size of the buffer cache 2

[MikeLacey]

In a competing version of UNIX that I won't name (HPUX) you have the option of having a dynamically sized buffer cache or a fixed size buffer cache. Fixed size is useful with DB Server only machines.

I can't find a way to specify a fixed size, am I just missing it?
Mike
michael.j.lacey@ntlworld.com

 

[MikeLacey]

Still got a problem with this.... anyone? Mike
michael.j.lacey@ntlworld.com
Email welcome if you're in a hurry or something -- but post in tek-tips as well please, and I will post my reply here as well.

 

[PSD]

Mike,

Can I assume that you have looked at configuring buffer cache from within the sys0 parameters : i.e. Max. no of pages in I/O buffer cache.

Outline what you already looked at and I will see if I can help??

Cheers

PSD
HACMP Specialist

 

[MikeLacey]

In smitty the help says:

Parameter: "Maximum number of pages in block I/O BUFFER CACHE"

"This buffer cache is used for reads and writes to block special files but is used minimally by the file system."

Surprised me a bit... "used minimally by the file system"

I think I need to do some more reading -- My goal is to provide the best environment for multiple Oracle DB's and, reading a book on optimising HP UNIX machines, I found the tip that a fixed size buffer cache is best for DB servers. Can you reccomend an AiX optimisation book/web site? Mike
michael.j.lacey@ntlworld.com
Email welcome if you're in a hurry or something -- but post in tek-tips as well please, and I will post my reply here as well.

 

[PSD]

Mike,

Take a look at the following book it really is very good:

AIX performance tuning by Frank Waters.

Here is the gen on maxbuf:

Purpose: Number of 4K pages in the block I/O buffer cache
Change: chdev -l sys0 -a maxbuf=newvalue
Tuning: This parameter normally has little performance impact on an AIX system since ordinary I/O does not use the block I/O buffer cache.

In short Mike if you use JFS this tuning parameter will have no real effect - the filesystem will use the filesystem buffer cache i.e. vmtune parameters...

I am not sure that it means by normal I/O I assume this means JFS, therefore is you use raw lv's this may be of some use......

In effect in Solaris/HP this parameter may help but in AIX it is mainly redundant though JFS...

I hope that this helps?

Cheers

PSD
HACMP Specialist

 

[MikeLacey]

Thx PSD <smile> Mike
michael.j.lacey@ntlworld.com
Email welcome if you're in a hurry or something -- but post in tek-tips as well please, and I will post my reply here as well.

 

[francs]

You should have said from the begining you wanted to tune Oracle settings.
Check out the following redbook:
Database Performance on AIX in DB2 UDB and Oracle Environments, SG24-5511-00

http://www.redbooks.ibm.com/redbooks/SG245511.html

 

[MikeLacey]

Thx Francs, I'll take a look. Mike
michael.j.lacey@ntlworld.com
Email welcome if you're in a hurry or something -- but post in tek-tips as well please, and I will post my reply here as well.