topic Re: Error while changing dbc_max_pct value. in Operating System - HP-UX

Error while changing dbc_max_pct value.

TanmayB — Tue, 05 Dec 2006 19:50:03 GMT

Hi,

While changing the dbc_min_pct value online I and geting below error message. I am using rx7640 and 11.23 hp-ux

*****dbc_min_pct and dbc_max_pct cannot be set dynamically because a static buffer cache is enabled. *********
What is the kernel parameter for static buffer cache?
How to change the value and is it online change?

Re: Error while changing dbc_max_pct value.

James R. Ferguson — Tue, 05 Dec 2006 19:56:53 GMT

Hi:

To use a dynamic buffer cache described by 'dbc_min_pct' and 'dbc_max_pct', you must set 'nbuf' and 'bufpages' to zero (0).

If you want a static buffer cache on 11.23, set both 'dbc_min_pct' and 'dbc_max_pct' to equal values.

Regards!

...JRF...

Re: Error while changing dbc_max_pct value.

TanmayB — Tue, 05 Dec 2006 20:00:41 GMT

JRF,

In my system the dbc_min_pct and dbc_max_pct value are same. If I want to change can I change it online?

Re: Error while changing dbc_max_pct value.

Dennis Handly — Wed, 06 Dec 2006 02:59:21 GMT

>dbc_min_pct and dbc_max_pct value are same. If I want to change can I change it online?

If you use kctune to look at these, both say "Immed".

Re: Error while changing dbc_max_pct value.

TanmayB — Wed, 06 Dec 2006 10:00:16 GMT

Though both say Immediate, but while changing it throws error message "dbc_min_pct and dbc_max_pct cannot be set dynamically because a static buffer cache is enabled."

Re: Error while changing dbc_max_pct value.

Patrick Wallek — Wed, 06 Dec 2006 10:07:37 GMT

That means that both bufpages and nbuf are set. Setting those 2 parameters sets your buffer cache at a static level. This mean that the dbc_man/max_pct parameters are no longer needed.

If you want to change your buffer cache now you must change bufpages and nbuf.

Re: Error while changing dbc_max_pct value.

spex — Wed, 06 Dec 2006 10:21:15 GMT

Hello,

bufpages and nbuf are static parameters, so in order to change them to 0, you will have to recompile your kernel and reboot.

PCS

Re: Error while changing dbc_max_pct value.

Steve Steel — Wed, 06 Dec 2006 10:25:17 GMT

Hi

http://docs.hp.com/en/939/KCParms/KCparam.FilesysParamsList.html

steve Steel

Re: Error while changing dbc_max_pct value.

TanmayB — Wed, 06 Dec 2006 13:35:29 GMT

nbuff and bufferpage is not supported in 11.23 (I think), as I could not get those.

Re: Error while changing dbc_max_pct value.

spex — Wed, 06 Dec 2006 14:09:47 GMT

They're supported, just deprecated, and will be obsolete in future releases.

$ uname -r
B.11.23
$ /usr/sbin/kctune nbuf bufpages
Tunable Value Expression
bufpages 0 Default
nbuf 0 Default

According to http://docs.hp.com/en/5990-6737/ch04s06.html:
* All tunables associated to the buffer cache (nbuf, bufpages, bufcache_max_pct, dbc_min_pct, and dbc_max_pct) are still supported through HP-UX 11i v2, but will be obsolete in future HP-UX releases. The dbc_min_pct and dbc_max_pct tunables will be replaced with new dynamic tunables that will control the amount of memory to be used for file caching in general (for caching file I/O data and metadata).

PCS