topic Re: memory issue in Operating System - HP-UX

memory issue

Michael O'brien_1 — Fri, 10 Aug 2001 09:29:54 GMT

Hi,

I've recently take over administration of a L-class 2000 server running Apache and Oracle apps server 11i (it's also been installed as 64bit), I suspect that the configuration is not being optimised and the performance maybe poor.

I've read several threads regarding swap and pseudo_swap, I would appreciated if anyone could advise me on weather I should enable pseudo swap and what I should set my dbc_max_pct kernel parameter too.

The current setting of the system is,

2GB Physical memory
3GB Disk swap

dbc_max_pct= 40
Pseudo swap is on

I ran glance and got the following reads.

Memory Utilisation = 100%
Swap Utilisation = 53%
Pseudo_swap = 1.5GB of which 866mb is utilised.

Thanks
Michael

Re: memory issue

Marcin Wicinski — Fri, 10 Aug 2001 09:42:36 GMT

Hi,

as far as I know this situation indicates that the system is swapping and you need to install additional amount of phisical memory. You can perform swapinfo and sar with -w option to watch swapping

later,

Re: memory issue

Carlos Fernandez Riera — Fri, 10 Aug 2001 09:59:57 GMT

run:

UNIX95= ps -aef -o "pid,user,comm,sz" | sort +3.0 -n

List process in order of memory comsum.

Re: memory issue

Praveen Bezawada — Fri, 10 Aug 2001 11:53:17 GMT

Hi
My first suggestion would be
dbc_max_pct is high, as you have 2Gb of memory as value of 200-300B for buffer cache would be ok i guess.
so 10-15% would be fine I guess.

..BPK...

Re: memory issue

Jerry Zhang — Fri, 10 Aug 2001 12:26:36 GMT

It may not be as bad as you think.

You can estimate total resident memory size (RSS) on the system by

$ ps -elf |awk '{print $10}'

it gives RSS for all processes in 4MB pages.
Rest of the memory are used by pseudo swap/buffer cache. Dynamic buffer cache has lower priority than processes - it will release memory if a process requests it.

You may reduce dbc_max_pct from 40 to 10 or 15.

Re: memory issue

Sundar_7 — Sat, 11 Aug 2001 09:58:18 GMT

Hi,

As the memory is big enough..U can obviously

enable psudeo_swap..

U can try

# kmtune -s swapmem_on = 1

and then rebuild the kernel..

U can try setting the

dbc_min_pct = 5 and dbc_mac_pct_25.

and then increase the dbc_max_pct according

to the performance..

Also make sure

nbuf and bufpages are set to 0 so that

Dynamic Buffer will be enabled..

Hope this helps

Sundar

Re: memory issue

A. Clay Stephenson — Sun, 12 Aug 2001 15:17:58 GMT

Hi Micheal,

In your case, I think you will actually see better performance if you disable dynamic buffer cache and set bufpages to about 80000
(~320 MB) and that is very, very generous.
If you measure, you find in the vast majority of cases that buffer cache hit rates and performance increase very,very slowly past this value. I suspect that you could drop it even more (~200 MB) and still get very good performance. If your are using raw/io or vxfs mount option convosync=direct,mincache=direct which bypass the unix buffers, you can drop even lower. Typically, it's better to use that memory in the SGA so that reducing buffer cache lets up pump up the size of the buffers within the SGA.

My 2 cents, Clay