topic Re: swap space size in Operating System - HP-UX

swap space size

Charles Holland — Fri, 11 Oct 2002 11:25:51 GMT

We have a small SAP shop with the OS being HPUX. After a receint upgrade check it was suggested that we increase our swap on our two L2000 machines. For three hours during our heaviest processing period one night we took a
swapinfo picture every 5 minutes. attached is one of the logs that was createcd on one of the machines. I'd like to get other peoples ideas if they think it is necessary to increase the swap. I personally don't, but thought I'd throw it up for discussion.

Re: swap space size

Alan Casey — Fri, 11 Oct 2002 11:29:20 GMT

Hi

This looks like you have plenty of swap space
There is not need to increase it based on this data.

Re: swap space size

Clemens van Everdingen — Fri, 11 Oct 2002 11:31:33 GMT

Hi,

Looks like there is no need to increase swap at all.
Looks fine to me, base on this figures.

C.

Re: swap space size

BFA6 — Fri, 11 Oct 2002 11:39:47 GMT

Hi,

I would agree. I can't see that you need anymore swap space.

Hilary

Re: swap space size

Donnie Darko — Fri, 11 Oct 2002 11:41:30 GMT

Hi,

Swap seems OK.

It's look like a performance problem.
Take a look on http://www.docs.hp.com/hpux/onlinedocs/os/11.0/tuningwp.html

Regards

Re: swap space size

Pete Randall — Fri, 11 Oct 2002 11:41:39 GMT

As it would appear that you never used any of it, I would have to say you've got plenty.

Pete

Re: swap space size

fg_1 — Fri, 11 Oct 2002 11:42:25 GMT

Looks as though you have 2.5X physical memory for swap space, that is plenty for that type of system even with a resource intensive program such as SAP.

I would not touch a thing here.

GL.

Re: swap space size

Eric Hess — Fri, 11 Oct 2002 14:21:16 GMT

You may want to set your external disk swap to be a pri=1. Besides that I would not touch swap. You system looks good as far as swap goes.

Re: swap space size

Bill Hassell — Fri, 11 Oct 2002 17:59:44 GMT

SAP recommends massively oversized swap areas which are never used when SAP is running. Typically, SAP will need just a few Gb of swap space (assuming you have several Gb of RAM (4 or more). During SAP installation (only) however, you may need 20 to 50 Gb of swap space that actually gets used. As you see from swapinfo, you are using 0% swap so you might as well return all but one of the swap areas back to the volume group and use the space for something real.

There will be only one symptom when you don't have enough swap space: swapinfo will report 90% or higher usage and processes will fail with out of memory errors.

Re: swap space size

Dave Wherry — Mon, 14 Oct 2002 12:52:27 GMT

What version of SAP are you running? As Bill said SAP requires or at least suggests you have a ridiculous amount of swap space. At version 3.1 I've seen SAP not start if the system did not have 3 times memory plus another 500MB. I could never prove it, but I suspected that SAP did some checks at startup and simply abended if it did not find enough swap. I had 8GB of memory and it never swapped either.
This past weekend our shop added another 8GB of memory so our swap requirement would now be 48.5GB. Keeping in mind that more memory means a lower chance of swapping, the SAP recomendation is just crazy.

Re: swap space size

Ian Dennison_1 — Mon, 14 Oct 2002 13:00:44 GMT

Charles,

Something to bear in mind is that this lack of Swap space will possibly show up on your Earlywatch as a Traffic Light.

If you have SAP Support arranged through an Agency, raise the issue of Swap Space requirements with them, or on OSS, and get in writing what their recommendation is (if it is different to the standard).

Some SAP Support Agencies have been known to dismiss functional problems as a 'lack of memory'; be aware that not following the SAP Swap Space recommendation can sometimes (not always!) result in this sort of response. This was a couple of years ago; I hope they have improved their levels of service since then.

Get the impression I did not enjoy my time in SAP Basis?

Share and Enjoy! Ian

Re: swap space size

Charles Holland — Mon, 14 Oct 2002 13:01:47 GMT

Thanks to all. It appears that everyones thoughts were pretty much the same as mine.

Bill - You made a point... maybe they recommend that much swap for an install... can't see it for a running system.

Dave - Current version is 4.5B. Just upgraded our database over the weekend to accomidate the upgrade to 4.6C. This will occur WE of 11/8/2002.