topic Re: UNIX buffer cache limit in Operating System - HP-UX

UNIX buffer cache limit

Dan Moloisane — Mon, 17 Oct 2005 06:45:36 GMT

I have a 40 GB RAM, 16 X 1000GB CPUs rp7420 server.
I need to tune the UNIX buffer to a most recommended size.

PLS advice on how much can you set the size.

Re: UNIX buffer cache limit

RAC_1 — Mon, 17 Oct 2005 06:48:37 GMT

Depends on what you run on the system.
With oracle, I tune it max to 800mb. ORacle does it's own buffering, so setting it at 800mb is enough for OS cache buffering.

Also I set dynamic cache. Use of dbc_max_pct and dbc_min_pct

Re: UNIX buffer cache limit

Arunvijai_4 — Mon, 17 Oct 2005 06:59:30 GMT

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=721990
http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=954245

Some good threads to learn ..

-Arun

Re: UNIX buffer cache limit

Stuart Abramson — Mon, 17 Oct 2005 08:56:40 GMT

We always set dbc_max_pct to 10%. (min defaults to 5% I think.) But you have a BIG RAM, and may not need that much. Start with 10% and see how it goes.

Re: UNIX buffer cache limit

Geoff Wild — Tue, 18 Oct 2005 07:26:53 GMT

You can hard net nbuff to 800 MB...

And/or just set the dbc_max_pct and dbc_min_pct to a setting that works out to somewhere between 500 - 800 MB of ram....

2% for max and 1 % for min would work.

Rgds...Geoff

Re: UNIX buffer cache limit

Ted Buis — Tue, 18 Oct 2005 09:32:32 GMT

If you have OnLineJFS, there are mount options so that you can avoid double buffering from Oracle and HP-UX which wastes RAM and time doing memory to memory transfers.

Re: UNIX buffer cache limit

Dan Moloisane — Thu, 20 Oct 2005 07:27:13 GMT

Thanks Guys for your effort.

Re: UNIX buffer cache limit

Andy Torres — Thu, 20 Oct 2005 07:51:23 GMT

This attachment has great info on tuning buffer cache, as well as other commonly misconfigured resources:

http://docs.hp.com/en/5580/Misconfigured_Resources.pdf

Re: UNIX buffer cache limit

Dan Moloisane — Mon, 24 Oct 2005 05:20:33 GMT

Thanks for the responses.
One more question,
I have OlineJFS currently installed on HP11.11. I need Oracle 9.2.0.4 to bypass UNIX buffer cache.What commands and options do I need to use and can it be done online while the database filesystems are mounted and Oracle is running.

Re: UNIX buffer cache limit

Orhan Biyiklioglu — Mon, 24 Oct 2005 05:25:49 GMT

Check this thread:

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=248308

hth

Re: UNIX buffer cache limit

RAC_1 — Mon, 24 Oct 2005 05:30:17 GMT

The options that you require are convosync=direct and mincache=direct. This can not be done online. (in fact there -o remount option, but does not make sense in your case)

Mount with above options.

Re: UNIX buffer cache limit

Jean-Luc Oudart — Mon, 24 Oct 2005 05:40:41 GMT

Hi

just a note. You should patch your Oracle database server to latest.
9.2.0.7

cf Metalink Note:189908.1 "ALERT: Oracle9i Release 2 (9.2) Support Status and Alerts"

Regards
Jean-Luc

Re: UNIX buffer cache limit

Tim Sanko — Mon, 24 Oct 2005 13:01:28 GMT

Dan,

What it really depends on is your mass storage. Is it an EMC DMX, if so minimize your buffer cache as it is basically irrelevant. If it is on a jbod, max it as far as you can and still have stuff work...

The real key is to look at the wait states and check sar while the DB is running.

If there is an unacceptable number of disk io waits, it is time to bump up the buffer cache.

If it has a low amount of hits it may not matter about the way things are configured...

run sar -a and check the memory stats, disk stats and cpu stats...

Tim

Re: UNIX buffer cache limit

Dan Moloisane — Tue, 25 Oct 2005 03:23:23 GMT

Ok, my dbase runs as a package on a cluster environment. How do I add the meancache=direct and convsync=direct options within the package control file.
The line looks like this within the control file:
LV[3]=/dev/vg01/lvol4;
FS[3]=/mp2hc500/pgt1/dbase01; FS_MOUNT_OPT[3]="-o rw"; FS_UMOUNT_OPT[3]=""; FS_FSCK_OPT[3]=""; FS_TYPE[
3]="vxfs"

Thanks