topic Re: swap in Operating System - HP-UX

swap

Carme Torca — Fri, 12 Dec 2003 09:54:28 GMT

Hi,

I have a system that have a high ratio of swap.
> swapinfo -tam
Mb Mb Mb PCT START/ Mb
TYPE AVAIL USED FREE USED LIMIT RESERVE PRI NAME
dev 1024 342 682 33% 0 - 1 /dev/vg00/lvol2
dev 1024 0 1024 0% 0 - 2 /dev/vg00/lvol11
dev 1500 344 1156 23% 0 - 1 /dev/vg00/lvol10
reserve - 1954 -1954
total 3548 2640 908 74% - 0 -

Physical Memory is: 3145728 Kbytes.
dbc_max_pct 10 and dbc_min_pct 1, and swapmem_on is 0.

Could I put swapmem_on = 1, and dbc_max_pct 30 and dbc_min_pct 5 to increse the performance in the system?

Could I do o see anything more in the system to increse the performance of memory or isn't any more to do?

Thanks!,
Carmen.

Re: swap

Mark Grant — Fri, 12 Dec 2003 09:57:00 GMT

Carmen

Bite the bullet and get more RAM. You may tweak it a bit but you need to find around 1GB of "RAM tuning" here.

Re: swap

Patrick Wallek — Fri, 12 Dec 2003 09:57:48 GMT

Since you are paging out to your swap area, there are really only 2 things you can do to increase performance:

1) Decrease memory load.

2) Increase the amount of available RAM.

swapmem_on would not help here and probably neither would messing with buffer cache.

Your best bet would be to add more RAM to this machine.

Re: swap

Carme Torca — Fri, 12 Dec 2003 10:01:42 GMT

ok,
And who do you know that I need 1 GB's RAM more? is there any calcul?
Thanks!

Re: swap

Mark Grant — Fri, 12 Dec 2003 10:05:53 GMT

You are using a third of one gig of swap on one device and 23% of one and a half gig on the other. Ok, not exactly a gig but getting there.

Re: swap

doug mielke — Fri, 12 Dec 2003 10:20:07 GMT

swapmem_on would not change anything now, but it could make things worse as you add more load, in thatr it will allow a little bit more processing load, where now, a process will error if it can't reserve swap space.

I've never seen a valid formula for determining ram size, If you swap at all, as you are, ram is the answer. It's likely more trouble that it's worth to add anything less than 1G, so that's a good start. The next place to look is to get details from the application vendors for recommendations, although they too will be suspec, but a good start.

Re: swap

Kevin Wright — Fri, 12 Dec 2003 17:28:36 GMT

I would set swapmem to on, the system will reserve space from the this area. That should help your swap space.

Re: swap

Alex Ostapenko — Tue, 16 Dec 2003 08:31:57 GMT

Dear Carmen --

Before concluding that you need more physical memory, verify that you have memory pressure by looking at "vmstat" output particularly the "po" (page-outs) and "sr" (scan rate) fields. "po" indicates that you are paging out, but that number also includes buffer cache sync and memory mapped output. Consistently high "sr" indicates that the page daemon is starting to work to find and/or free up pages for a process that needs it. If one or both these numbers are consistently high (2-3 digits), then you probably have memory pressure and you need more physical memory. If both these numbers are consistently low, that means that you may have a lot of process virtual memory allocated causing the high swap utilization, but that they're not all trying to access the memory at the same time. And that would mean that you're getting your money's worth with memory. General recommendation is that swapmem_on should be set to "1" regardless. Good luck!

=:-) Alex