topic Re: dbc_min/max_pct in Operating System - HP-UX

dbc_min/max_pct

C_VOIP — Thu, 31 Aug 2006 13:33:13 GMT

I have an SA that has set these parameters to the following values. I am suspect as to the effectiveness. The box is the main Oracle DB box in an APPS/DB architecture. Any input would be appreciated.

kmtune -q dbc_min_pct
Parameter Current Dyn Planned Module Version
===============================================================================
dbc_min_pct 5 - 5
[/opt/oracle]: kmtune -q dbc_max_pct
Parameter Current Dyn Planned Module Version
===============================================================================
dbc_max_pct 5 - 05

Re: dbc_min/max_pct

Robert Salter — Thu, 31 Aug 2006 13:38:34 GMT

Most of the Oracle servers I've worked with use
dbc_max_pct 5
dbc_min_pct 5

Oracle manages it's own memory.

regards,

robert

Re: dbc_min/max_pct

Patrick Wallek — Thu, 31 Aug 2006 13:45:52 GMT

This is effectively setting a static dynamic buffer cache of 5% of RAM.

This could have been done more easily with nbuf & bufpages.

Re: dbc_min/max_pct

David Child_1 — Thu, 31 Aug 2006 13:51:03 GMT

Hello Dave@Comcast;

Admins will often set dbc_min/max_pct to the same value. This will essentially disable the dynamic cache stuff and just set aside a predefined amount. The number used is dependant on the amount of memory you have on your server because this is just a percentage of that. So if your server has 8GB of RAM you would have ~400MB of cache set up using the 5% value you have.

There really isn't any need for much more than 512MB of cache set up for an Oracle database server (especially on 11.00 and lower where excessive buffer cache can actually affect performance negatively).

David

Re: dbc_min/max_pct

A. Clay Stephenson — Thu, 31 Aug 2006 15:04:04 GMT

The 5% value is a bit meaningless w/o knowing the amount of physical memory in the box. In general, on an 11.0 box that is serving as a database server, you want to shoot for something in the 400-800MiB range provided that you have "lots" of memory. For 11.11 800-1600MiB is a better choice. If you are running raw/io and this is a pure database server then something in the 300MiB range is adequate. In order to provide better tuning, more data are needed. How much memory? Raw or cooked database i/o? SGA size's? swapinfo -tam output. Any pageouts observed?

Although it is being phased out, I still prefer static buffer caches set not by matching dbc-min_pct to dbc_max_pct but rather by setting bufpages to a non-zero value.

Re: dbc_min/max_pct

C_VOIP — Thu, 31 Aug 2006 15:42:23 GMT

Thanks All,
I have assigned points.

DD

Re: dbc_min/max_pct

Geoff Wild — Thu, 31 Aug 2006 15:54:17 GMT

That depends on the ammount of memory in the system.

For Oracle, it has it's own buffer cache.

Basically, you want it between 500 and 800 mb of memory..

So, if your system has 10GB of ram - then these are good values...

Rgds...Geoff