Re: HP-UX Buffer Cache

From: Gaja Krishna Vaidyanatha <gajav_at_yahoo.com>
Date: Fri, 23 Jun 2000 11:58:30 -0700 (PDT)
Message-Id: <10537.110320@fatcity.com>

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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