Error while changing dbc_max_pct value.

[TanmayB]

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?

[James R. Ferguson · Accepted solution]

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...

[TanmayB]

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?

[Dennis Handly]

>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".

[TanmayB]

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."

[Patrick Wallek]

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.

[spex]

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

[Steve Steel]

Hi

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


steve Steel

[TanmayB]

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

[spex]

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