topic Re: performance in Operating System - HP-UX

performance

medali.benchaabane — Mon, 18 Dec 2006 05:43:38 GMT

we have an rp8400 11iv1 with 20GB memory and 24GB of swap. kmeminfo shows 164MB free memory.

i have attached a file containing the output of kmeminfo, swapinfo and vmstat commands.

i have remarked the following
- pct of swap used is 4% of 24GB
- vmstat shows that there is no paging out

do we have a performance problem or no ?

Re: performance

spex — Mon, 18 Dec 2006 07:36:35 GMT

Hi,

The attached textfile is empty.

You most likely have a dynamic buffer cache enabled. This means that up to dbc_max_pct percent (50% by default) of your free memory will be assigned to the OS buffer cache.

To change to a static buffer cache, assign a value to bufpages, recompile your kernel, and reboot. For your system, I'd recommend at least 1GiB for this purpose (256 pages w/a 4MiB pagesize).

As you indicated, there is no paging taking place, and hardly any swap being used. As long as your users are happy, and you have happy with other performance metrics (e.g. IO to disk) there isn't a performance problem.

PCS

Re: performance

medali.benchaabane — Mon, 18 Dec 2006 08:16:10 GMT

here is the file attached

max_dbc_pct is 5%

Re: performance

spex — Mon, 18 Dec 2006 09:23:47 GMT

Hello,

Still nothing attached.

Please paste the output of:
# UNIX95= ps -e -o 'vsz,args' | sort -rn -k1
into your reply.

Also, in my previous message, I meant to say 4KiB, not 4MiB, as the pagesize in HP-UX. For a desired static buffer cache of 1GiB, this results in 262144 pages (1073741824/4096).

PCS

Re: performance

Rita C Workman — Mon, 18 Dec 2006 09:35:06 GMT

You are not showing paging out, your swap utilization is low.....

Cause I don't see a problem here !

Are users complaining ? Do you have applications choking ? Are you getting any specific kind of error messages in your syslog ? Is your DBA saying there's an issue ?

Can't help, when we don't see a problem...

Rgrds,
Rita

Re: performance

Jon M Zellhoefer — Mon, 18 Dec 2006 11:26:46 GMT

Not only dbc will use memory, but applications like Oracle etc will allocate swap and not use it. This is a reserved space that the app creates in the event that it needs to be paged out of memory due to a performance issue or application conflict. I have seen many systems in the past that show up to 80% swap util with no paging - this is just a reserve allocation and not usually a performance issue. If you are actively paging, then it's time to take a closer look. Also keep an eye on swapmem ... if this is set on, you'll see swap reserve or swap active space allocated out of physical memory - not a bad thing unless you're having issues running out of phys mem, but something to remember when you're looking at overall performance issues.