Re: HP-UX Buffer Cache

• The kernel parameters Gaja refers to are dbc_pct_min and dbc_pct_max. There is also another trick: if you set the kernel parameters nbuf and bufpages to values different from 0, you will set the value of the buffer cache, whatever the values in dbc_min_max and dbc_pct_min. The cache will have a static size instead of being dynamic.
• If you keep it dynamic, decreasing dbc_pct_max is advisable, but dbc_pct_min should be kept at 5-10% because you may not need that much memeory, so it does harm to release it when not not needed, especially if you use the VxFs mincache option (see below)
• If you installed your Oracle file on jfs (VxFs) and purchased the Advanced jfs product, you can use a handy mount option: - o mincache=direct. This tells the system to bypass the buffer cache for this fs.

HTH Christian Bilien
christian_at_open-seas.com
www.open-seas.com

• Original Message ----- From: Gaja Krishna Vaidyanatha <gajav_at_yahoo.com> To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> Sent: Saturday, June 24, 2000 12:28 AM Subject: Re: HP-UX Buffer Cache

> Ed,
>
> This is a classic memory hog problem with a lot of systems out
> there running HP-UX, where the kernel has not been customized.
> The default kernel settings allow the O-S to procure upto 50% of
> available memory for the file system buffer cache. This can and
> will cause severe memory starvation during times with very heavy
> load on the system. As a result of the memory starvation, the
> system will experience a significant amount of paging and
> swapping (in the H-P world it is also known by the term -
> process deactivation).
>
> Been there in your shoes and it is not fun. The fix to this is
> to modify the relevant parameters (DBC...MIN and DBC...MAX ??)
> to 15%, so that no more than 15% of memory is allocated for the
> file system buffer cache. It is true even for systems that do
> not use raw devices. You can make these changes using the "SAM"
> utility.
>
> Best Regards,
>
> Gaja.
>
> --- Ed Bittel <ebittel_at_yahoo.com> wrote:
> > I have a HP9000 server running HP-UX 11.0 with Oracle 8.0.5.
> >
> > I've been reviewing memory usage stats with my SA. Our server
> > has 2GB of physical memory, with 1GB reserved for the HP-UX
> > buffer cache and 1GB available to users (i.e., Oracle). I've
> > read in the Administrator's Reference manual, that Oracle does
> > not need to use the HP-UX buffer cache if the system is using
> > raw devices. I have been unable to find any good information
> > on how to size the HP-UX buffer cache when using file systems.
> >
> >
> > Because we're getting a little tight on memory, I'm wondering
> > if it is possible and/or advisable to reduce the size of the
> > HP-UX buffer cache to free up additional memory for user
> > processes. What effect would this have on system and database
> > performance? Any other recommendations or comments on this
> > subject would be appreciated.
> >
> > Thanks,
> >
> > Ed
> >
>
>
> =====
> Gaja Krishna Vaidyanatha | gajav_at_yahoo.com
> Brio Technology | (972)-304-1170
>
> "Opinions and views expressed are my own and not of Brio Technology"
>
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Received on Sat Jun 24 2000 - 02:15:35 CDT