topic 11.31 Buf Cache vs Filecache in Operating System - HP-UX

11.31 Buf Cache vs Filecache

Francis Noël — Mon, 14 Jan 2008 20:54:51 GMT

Hello forum people.
Two questions for you today :)
About an rx3600 under 11.31

I need to get up to speed with some of 11.31's terminology.

A peek at the memory report in Glance turns up some pretty interesting numbers :
Buf Cache: 0mb
FileCache: 418mb

I expected Filecache to be in that general region since I specified the filecache_min and filecache_max à 500MB but sould the Buf Cache read 0 ? Since dbc_max_pct and dbc_min_pct are gone in 11.31 I'm thinking this might just be an artifact in Glance ?

OK second question

Since this is to be an Oracle server I set the FileCache pretty low, betting on the SGA doing its thing and all. Upon installing nifty things like Oracle Application Server I noticed the memory subsystem got a little overwhealmed when the java installer was pushing files into the /opt filesystem. Namely Page Outs were happening and the disk hosting /opt (local sas) was pegged at 100%. Since I had plenty of physical RAM available at the time and that swapinfo showed only 17% of the pseudo-swap was allocated could this indicate that the server was, at that time, short on FileCache ?

Thank you for your time !

Re: 11.31 Buf Cache vs Filecache

VK2COT — Wed, 16 Jan 2008 08:03:52 GMT

Hello,

Firstly, there are several patches that are critical to performance on HP-UX 11.31.
How old is your build? I would do
an assessment and install patches if possible.

a) With the introduction of HP-UX 11.31, the
traditional Buffer Cache has been replaced
by the Unified File Cache (UFC).

The new sybsystem integrates the Memory
Page Cache and Buffer Cache to provide
coherency for file access.

b) I am aware of some discussions in
various forums and HP has an open incident
number that a different issue with file
cache in HP-UX 11.31. Basically, if
a file is written to file cache and closed,
subsequent file operations, such as
open() and unlink(), hang while the entire
file is flushed from the file cache.

There is also another issue when unaligned direct I/O is slow on HP-UX 11.31 when memory pressure exist.

I also know of some performance problems with
sequential writes to the file system. One
test site reported that turning on fcache_fb_policy helped.

Make sure that you have filecache_max set to
the right size instead of dbc_max_pct...

I will search for your type of problem
later this week (I am teaching HP-UX SNA I
and not much time is free for me).

I would suggest to contact your HP
representative and try to get:

HPjconfig for tuning kernel for Java applications

HPmeter to measure performance of Java applications

Caliper - general purpose application performance measurement/analysis tool

Cheers,

VK2COT

Re: 11.31 Buf Cache vs Filecache

Francis Noël — Wed, 16 Jan 2008 20:38:22 GMT

Hello Dusan and thank you for your reply.

System build is pretty current.
I installed the september 2007 release and all critical patches are installed (according to SWA).

If you are aware of any documentation pertaining to UFC I would appreciate a link.
Specifics on tuning the FileCache size would be welcome too.

Re: 11.31 Buf Cache vs Filecache

Francis Noël — Thu, 14 Feb 2008 21:04:23 GMT

Going to open a new thread, the issue has transmogrified itself.