topic Re: shmmax value in Operating System - HP-UX

shmmax value

Amit Manna_5 — Fri, 27 Feb 2009 17:06:24 GMT

I have a HP system OS version is 11.0 for
shmmax value is as follows:
kmtune -l -q shmmax
Parameter: shmmax
Value: 0XC0000000
Default: 0X4000000
Minimum: -
Module: -

Total VM : 1012mb Sys Mem : 244.7mb User Mem: 2.78gb Phys Mem: 4.00gb
Active VM: 257.9mb Buf Cache: 614.4mb Free Mem: 386.2mb

We are planning to upgrade the physical memory from 4 GB to 6 GB.

Do we need to increase the shmmax value and if yes to what value

What would be procedure for increasing it

many thanks in advance

Re: shmmax value

Johnson Punniyalingam — Fri, 27 Feb 2009 17:38:32 GMT

Hi Amit,

>>We are planning to upgrade the physical memory from 4 GB to 6 GB.<<

Your swap space should be double the size of your Pshyical RAM

if total Pshyical RAM 6GB you need have totol swap space of 12GB

# swapinfo -tam (Can check current size of you swap)

>>Do we need to increase the shmmax value and if yes to what value<<<

NO NEED

what Application are you running.?
do you have any perfromance issue?

Please below Thread for more Inforamtion

http://forums11.itrc.hp.com/service/forums/questionanswer.do?threadId=1272448

Thanks,
Johnson

Re: shmmax value

Mel Burslan — Fri, 27 Feb 2009 17:40:39 GMT

>We are planning to upgrade the physical
>memory from 4 GB to 6 GB.
>
>Do we need to increase the shmmax value and
>if yes to what value

The answe is it depends, but more than likely it will be to your benefit to increase this value.

Most java-heavy applications running on hpux (and what is not java-heavy nowadays) wants you to set shmmax value to value which is equal to the amount of physical memory. Right now, you are saying you have 4GB physical memory on the system but your shmmax is set to 3GB. If it is configured like this for a reason, you need to figure out why it is that way and adjust the value according to the requirements of the person/vendor who wanted it that way. This will help you avoid headaches down the road.

If you are running Oracle, SAP, or any other java written application, in the lack of finding out what shmmax value needs to be, it is a safe bet to set it to the amount of physical memory, which will be 6GB in your case. SO the command to modify it should be as follows:

kmtune -s shmmax=6442450944

ans it is a dynamically configurable parameter, not needing a reboot.

Hope this helps

Re: shmmax value

Tingli — Fri, 27 Feb 2009 18:42:22 GMT

I think in oracle, the shmmax should be larger than the largest sga.

Re: shmmax value

Emil Velez — Sat, 28 Feb 2009 00:56:12 GMT

shmmax is the size of the largest shared memory segement that a program can create. A program can attach to multiple shared memory segments but this parameter is the largest size of a single shared memory segment.

Defer to your applications kernel parameter requirements.

Re: shmmax value

Amit Manna_5 — Wed, 04 Mar 2009 15:00:47 GMT

Does this parameter increase dont need reboot/

Re: shmmax value

Ganesan R — Wed, 04 Mar 2009 15:06:44 GMT

Hi Amit,

Changes to this tunable take effect immediately and does not need reboot.

Check this..

http://docs.hp.com/en/B2355-60127/shmmax.5.html

Re: shmmax value

Steven E. Protter — Wed, 04 Mar 2009 15:16:42 GMT

Shalom,

Do you need to increase shmmax? No.

It might improve performance of applications like Oracle.

In this case I would do as follows:
sam
Kernel
Configurable parameters
Change shmmax

Compile kernel and boot via the menu.

Note: HP-UX 11.00 is out of support. I strongly urge a make_tape_recovery or make_net_recovery backup be done before any changes.

SEP

Re: shmmax value

Sharma Sanjeev — Wed, 04 Mar 2009 15:34:49 GMT

Hi Amit

Its not required to increase the value of shmmax after upgrade of memory but you can always increase it.

Its a Static value and requires reboot in 11.00

Regards
Sanjeev

Re: shmmax value

Sharma Sanjeev — Wed, 04 Mar 2009 15:39:33 GMT

Hi Amit

As you mentioned hp-ux version is 11.00 and in this version shmmax is static

shmmax 3221225472 3221225472 Static N/A

but not in 11.23

so it will require reboot after changing the value

Regards
Sanjeev

Re: shmmax value

Shahul — Wed, 04 Mar 2009 15:50:13 GMT

Hi,

Just for the reason of upgrading physical memory, you don't need to increase Shmmax. Check with you application vendor what should be you shmmax. When you upgrade your physical memory, the good prachtice is to alter your swap and dump. Again it is not a hard and fast rule, it's all depending on your requirement.

Good Luck
Shahul

Re: shmmax value

Ganesan R — Wed, 04 Mar 2009 16:01:27 GMT

Hi Amit,

I didn't noticed that your OS version is 11.0. I though it is higher version. In all higher versions, shmmax can be increased dynamically.

Re: shmmax value

Amit Manna_5 — Fri, 06 Mar 2009 11:52:58 GMT

hi
Can we increase the kernel paramter in single user mode. If yes please let me know the process.

Re: shmmax value

Hein van den Heuvel — Fri, 06 Mar 2009 12:05:17 GMT

>> Can we increase the kernel paramter in single user mode. If yes please let me know the process.

Noop.
That's why it is called 'kernel' param.
One setting for all.

Hein.

Re: shmmax value

Sharma Sanjeev — Fri, 06 Mar 2009 12:23:31 GMT

Hi Amit

You can not change/increase in Single User mode :-)

Regards
Sanjeev

Re: shmmax value

Hein van den Heuvel — Fri, 06 Mar 2009 13:22:57 GMT

oh wait, I guess I was reading the last question wrong (shouldn't visit forums before first coffee). I read it as 'for a single user', but surely it was 'with the system in single user mode'.
Yes, you can do that. But you can just set the parameters to chance (kctune) on the running system, for the next reboot.

Hein.

Re: shmmax value

Avinash20 — Fri, 06 Mar 2009 13:38:13 GMT

On a running server

# kctune shmnax=

<< Above could be run without a reboot>

When you are ready with the downtime

# kmupdate
> Reboot the server

All the best

Re: shmmax value

Doug O'Leary — Fri, 06 Mar 2009 17:19:57 GMT

Wow; what an entertainingly contradictory thread!

First, lets verify the environment:

It's an 11.00 system on which he's upgrading ram for 4 gigs to 6 gigs.

A couple of the more entertainingly incorrect answers:

1. kctune is 11.23 and 11.31; not 11.00. kmtune is the right command.

2. swap does not have to be 2x ram. That is archaic thinking - although, in this particular case, since it's an archaic operating system with an archaic amount of ram, the 2x ram may be right.

The right answer for the shmmax parameter is it doesn't have to be upgraded and you should check with the vendor. If you're running oracle, it probably should be. *That* being said, you're also probably running an antiquated version of oracle. Versions prior to 8.1.6 (I believe?) couldn't access more than 4 gigs of shared memory in one swell foop anyway, so updating the shmmax beyond that point doesn't get you much - and, may, in fact, prevent oracle from starting.

Should you decide to do the kernel upgrade, it will require a reboot. If you ever upgrade to 11.23 there are significantly more dynamic kernel parameters. Yet more in 11.31. Those two OSes make kernel updates a breeze, though. Run the appropriate kctune commands, then run kctune -D to find out if you need a reboot.

Here's a checklist for command line kernel creation that I always use:

http://www.olearycomputers.com/ll/hpkernel.html

This applies to 11.11 and prior; as I said, the 11.23/11.31 kernel process is so easy it doesn't require a checklist.

Hope that helps.

Doug O'Leary

Re: shmmax value

Avinash20 — Fri, 06 Mar 2009 17:23:41 GMT

"kctune in 11.11"

Oops.. Need good sleep before replying to number of thread.
Will make a habit of reading the complete thread bfor answering.

Thanks Doug for catching it ..

Re: shmmax value

Dennis Handly — Fri, 06 Mar 2009 21:17:42 GMT

>Avinash: "kctune in 11.11" Need good sleep before replying to number of thread.

There is nothing wrong with mentioning kctune(1m) provided you put the right marketing spin on it. :-)
I.e. You can use kctune on 11.23 and shmmax is dynamic tunable so you don't have to reboot.