UNIX for Advanced & Expert Users

Neil,

Does your system have System Activity Reporting (SAR) in place?
That may provide some indicators to usage and when.

Humble suggestion

"Page faults" is a number that includes too many things to be very useful. I'm surprised that your vmstat bothers to display the number, although I see here that it does. Look instead at the page out rate (label=pout). If this number is high, that's your problem. Note that it is zero on the man page. Any non-zero number is not real good. And the higher the number, the worse it is.

Most versions of unix these days allocate just enough stack to store the environment and the arguments and then let the process page fault its way into memory. Does NT load the entire process into memory at start-up time?

We still did not address the swap issue....... but now it seems we are talking NT..... I have no idea if NT uses swap space.... .does it?

Actually, in this post and in again in this post he said that his 35 GB of swap is about 35% used.

Also, in this post he says: Since he is trying to leverage his NT experience to understand the behavior of his unix system, the difference between the two is important. I think that his NT experience is misleading him into thinking that that high page faults are problematic.

Got it... thanks. I was confused reading UNIX in one post and NT in others....not really paying close attention .... sorry for the confusion.....


Perhaps more RAM would help.........

Thanks for your replies everyone - much appreciated.

Cameron - unforunately, Tru64 only has the old subset of system tools - vmstat, iostat, etc. Unfortunately SAR isn't one of them. I've used SAR in the past and really don't like not having it!

Neo - yes, I'd love to order more RAM, but before we do so, it unfortunately needs to be justified! The only way that I can do that is to show that the statistics that we are getting are over a particular threshold.

Perderabo - thanks for the information about pages out (pout). Yes we do have entries in this column (around 5000 per minute using vmstat), however the same question still applies - is this too high and what should it be?!!

I do appreciate that if everything was in RAM then so much the better, but surely this is not essential. For instance, if we have, say, 1000 processes and around 250 of them are idle. If those 250 were in swap it wouldn't matter - paging would occur but it shouldn't be a problem. Obviously if only 600 processes could fit in RAM and the other 150 active transactions were also in swap, it may well be the cause of problems.

Hope this may be of assistance!!

Kind regards,

Neil

Actually sar is older than vmstat, iostat, etc.

5000 page outs per minute is 83 page out per seconds. Yes that seems high, especially if it's sustained. I would strive for zero. Unix does not load entire processes into core. By the time stuff is in core, it's there because it needs to be. No it's not essential to add more core, you can live with the slowness instead. It's not like anything is breaking. But you were looking for the source of the slowness and I think you have found it.

Talk to your memory salesman and explain the situation. He or she may be able to allow you to borrow a gig of memory for a week or so. I'll bet that you will see the slowness disappear. Then your management can decide whether or not to buy the memory.