Please help Memory Tuning

[Elder Silva_1]

Hi, my 8G of Physical Memory hpux 11i box is running with sybase with 6G shmmax.

Please help me with this coz i got 100% used in memory with i command swapinfo.

# swapinfo
Kb Kb Kb PCT START/ Kb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 16384000 0 4194304 0% 0 - 1 /dev/vg00/lvol2
reserve - 4065992 -4065992
memory 6621876 6621876 0 100%

Thanks!

[Ermin Borovac · Accepted solution]

Start by identifying processes that use most memory. 'sz' is process resident memory usage given in physical memory pages (page size is 4K).

$ UNIX95= ps -e -o sz,pid,user,args | sort -n

Also check your buffer cache size. By default, it is set to 50% of your total memory, which will work against you. Buffer cache size is controlled by kernel parameters dbc_min_pct and dbc_max_pct. You probably want to set dbc_max_pct to value between 5-10%.

[Sudeesh]

Hi,
From the swapinfo output we can see your psuedo swap is at 100%. Pseudoswap is simply an HP-UX mechanism to allow system with large amounts of memory to not require large amounts of swap.Pseudoswap is nothing more and nothing less than kernel bookeeping. With pseudoswap, processes are allowed to count 75% of memory + any "real" swap as swap space so that more processes can be run.

Coming to your problem:
I would like you to check following kerenel parameter.

dbc_max_pct

which set the buffer cache used to default 50% and can be a waste of memory. 500MB of buffer cache is enough in normal case.

Sudeesh

[Elder Silva_1]

Thank you so much! i got dbc_max_pct = 50

btw, how do i update the kernel? :)

what are the steps after i do

kmtune -s dbc_max_pct=5

thanks!

[Ermin Borovac]

Assuming hp-ux is 11i v1 (11.11), here are steps to recompile the kernel.

# cd /stand/build
# rm -r *
# cp /stand/system /stand/system.prev
# /usr/lbin/sysadm/system_prep -s /stand/system
# diff /stand/system /stand/system.prev
# kmtune -s dbc_max_pct=5
# /usr/sbin/mk_kernel
# kmupdate
# cd /
# shutdown -ry 0

[Devender Khatana]

Hi,

This can be easily done through SAM also. It is quite safe to do it with SAM.

SAM->Kernel Configuration->Configurable Parameters->
Select the parameter and double click. Chage value to desired value. Now from action click on process new kernel. Once done it will reboot your system.

HTH,
Devender

[Sudeesh]

On HPUX 11.23 this is dynamically tunable.

[rx260-05]/ >kctune dbc_max_pct
Tunable Value Expression Changes
dbc_max_pct 10 10 Immed
[rx260-05]/ >kctune dbc_max_pct=7
* The automatic 'backup' configuration has been updated.
* The requested changes have been applied to the currently
running system.
Tunable Value Expression Changes
dbc_max_pct (before) 10 10 Immed
(now) 7 7
[rx260-05]/ >kctune dbc_max_pct=7
[rx260-05]/ >kctune dbc_max_pct
Tunable Value Expression Changes
dbc_max_pct 7 7 Immed
[rx260-05]/ >



Sudeesh