topic Re: excessive paging in Operating System - HP-UX

excessive paging

Alan Buenaventura — Mon, 26 Aug 2002 05:56:33 GMT

Hi,

How do you monitor excessive paging? What is the reference value to say that execessive paging is occuring?

Thanks
-Alan

Re: excessive paging

Leif Halvarsson_2 — Mon, 26 Aug 2002 06:01:12 GMT

Hi
You can use vmstat with an argument (sample interval) to monitor paging.
Example: vmstat 5
See the man page for vmstat.

Re: excessive paging

Alexander M. Ermes — Mon, 26 Aug 2002 06:02:27 GMT

Hi there.
command is 'swapinfo -a'.
Shows, whether your machine is swapping on devices. If yes, think about the structure of the applications / databases you run.
Or buy more memory.
Rgds
Alexander M. Ermes

Re: excessive paging

Alan Buenaventura — Mon, 26 Aug 2002 06:15:43 GMT

Thanks Leif & Alexander, but how can I tell whether excessive paging is occuring, like from vmstat output, what would be the reference value of the page-in/page-out rate for normal and/or excessive paging.

-Alan

Re: excessive paging

U.SivaKumar_2 — Mon, 26 Aug 2002 06:47:39 GMT

Hi,
What is your dbc_max_pct and dbc_min_pct kernel
paramters values ?
Paging may not present as serious a problem as swapping, because an entire program does not have to reside in memory in order to run. A small number of page-outs may not noticeably affect the performance of your system.

To detect excessive paging, run measurements during periods of fast response or idle time to compare against measurements from periods of slow response.

Use vmstat to monitor paging.
added to the free list by page-out activity(po). This value should be zero.
If your system consistently has excessive page-out activity, consider the following solutions:

1)install more memory
2)move some of the work to another system
3)configure your kernel to use less memory by
tuning dbc_max_pct and dbc_min_pct

regards,
U.SivaKumar

Re: excessive paging

Leif Halvarsson_2 — Mon, 26 Aug 2002 07:34:56 GMT

As U.SivaKumar already have told there should be very low (or zero) po activity if evrything is OK. If you want a more "user-friendly" tool to monitor your system you can use the GlancePlus. This is licensed but there is a 60 days trial version on the HP-UX media.

Re: excessive paging

John Bolene — Mon, 26 Aug 2002 12:45:55 GMT

You can also use top to see if swapper is using more than 1% of CPU. If it is up to 5 or 10%, there is a lot of memory swapping going on.

This solution does not require any money to be spent.

Re: excessive paging

Bill Hassell — Mon, 26 Aug 2002 13:08:16 GMT

The most important value is po (page out). pi (page in) counts program starts as well as page in from swap and there is no way to separate the two, so ignore page in. The absolute numbers are typically: less than 10, ignore it, paging is very low. Between 10 and 50, the page out numbers are getting high but is it steady? Having a page out rate of 75 once every hour isn't of much concern, but a page out rate of 25 that is always occurring means you are out of RAM most of the time.

Numbers in the 100's indicate a fair amount of paging and more RAM is definitely advised but as always, a large burst once a day may be acceptable.

Re: excessive paging

Alan Buenaventura — Tue, 27 Aug 2002 01:09:05 GMT

Thanks Bill, that's an enlightenment.
Thanks to all who helped. Now for the points.... :-)

-Alan