Unix- Paging Rate

[RichaAg]

Is there any optimum value for paging rate? Can a paging rate of 30-40 be condidered high?

[Patrick Wallek]

If you are talking about page outs (PO column in sar), then yes 30-40 is high!!

As far as I am concerned then ANY value other than 0 is too high!

[Bill Hassell]

"Paging rate"

A bit ambiguous for HP-UX. Every program starts on disk and when first started, the program is paged into memory (the pi metric in vmstat). A program that may have been paged out to the swap area will be paged in when activated again. Therefore, the page in rate may be in the hundreds but not particularly useful.

Page out is very different. It measures the pages sent to the swap area -- and as Patrick said, zero is the best value. This is accomplished by having plenty of RAM. My rule of thumb is:

1 digit (0-9) pageout is fine
2 digits (10-99) pageout is not good
3 digits (100+) Your system is thrashing, that is, paging out like crazy.

Page out is particularly disruptive. First, a low priority program must be stopped and then deactivated. When a higher priority program is ready to continue but out in swap, the low priority program's data and stack area will be written to the swap area. During that time, because memory is being reorganized, a spinlock will be required to prevent other processors from rearranging memory. Similarly, spinlocks will occur as the paged program is rolled back in.

All of this impacts all the processes currently running. If this happens frequently, nothing gets done (just swap thrashing) and performance is awful.

So, yes, page rates 30-40 over several minutes or hours is high. Get more RAM (at least twice as much).

[avizen9]

its interesting question,
Bill has provided very good detail info here.

I just work around and found below url on hp doc site,

http://docs.hp.com/en/1219/tuningwp.html
check under Memory section, having good info,

[Turgay Cavdar]

For hp-ux 11iv3 page out values are somehow different.Page-out activity doesn't mean lack of memory,the page-out statistics now include file cache memory operations.

"The vhand daemon uses a software technique called Cache Aging to maintain an optimal working set of file data in memory. Therefore, vhand keeps track of pages that have been accessed recently and of those that have not. Pages that have not been accessed recently are better candidates to be reclaimed. It is assumed that if pages have not been accessed in the recent past, they will not be accessed in the near future. When vhand reclaims pages, it may need to flush (page-out) modified data to the files before it can actually release the pages to the pool of free memory."

http://h71028.www7.hp.com/ERC/downloads/4AA0-7157ENW.pdf