Excessive Page INs


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Operating Systems AIX Excessive Page INs
# 1  
Excessive Page INs

Gurus,
What does excessive Page Ins indicate for the memory status on the machine.

Or, in another form, Reardless the OS, does excessive Page INs reflects memory shortage ?
# 2  
Gee, normally you see complaints about excessive page-outs. My background is more in Solaris, where there isn't the distinction between "paging space" and "swap space" that AIX makes, so take this with a grain of salt.

The rule of thumb is that paging space should be 2x RAM. Disk space is cheap, RAM is more expensive. If paging space is more than 2x RAM, performance will be poor (if you start using all that virtual memory). You could have a smaller paging space than RAM, say 1x RAM, but as disk is cheap, most people just mindlessly setup 2x RAM and be done with it. If you need more virtual memory, you need more RAM, becuase simply adding more paging space is just going to make performance bad.

Does that help?
# 3  
Garry, so paging in doesnot mean memory shortage as i understand ?

Then, what is the difference between paging space and swap space 'even in AIX, Tru64 or Solaris'.
# 4  
i would guess that page-ins WOULD be a memory shortage.... because eventually that would result in page-outs.

the way i learned it (a long time ago), the general rule is use 2x paging space up to a certain limit (like 1GB or something like that). start with, say 1x or 1.5x, then run your application, then run the 'lsps -a' command to see utilization. once you start hitting into the solid double digits (like 30 to 40% or more), then you may want to consider installing more memory. trust me... you DO NOT wanna even come close to 100%. give your self plenty of buffer.

paging space in AIX is the same as swap space on solaris.
# 5  
Sorry I wasn't more clear. Yes, I think paging messages do indicate a memory shortage. I discussed the 2x RAM rule of thumb because I was thinking you could see how much RAM you have, and see how much paging space you have. If you have more than 2 times as much paging space as RAM, then that's why your performance is bad.

ScatterBrain - Making a scientific determination of how much RAM you need? Boy there is a lost art. I can't recall the last time a machine got ordered who's specifications were determined as opposed to guessed at. :-)
# 6  
Quote:
Originally Posted by Garry_Garrett
ScatterBrain - Making a scientific determination of how much RAM you need? Boy there is a lost art. I can't recall the last time a machine got ordered who's specifications were determined as opposed to guessed at. :-)
hahahhaa... i hear ya, bud. the problem nowadays is that from the perspective of "sizing", you're at the mercy of your application vendor. Smilie
# 7  
Negm, be aware that there is a fundamental difference between AIX versions prior to 4.3.3 ML10 (aka "AIX 4.4") and after this version. Before 4.3.3 ML10 AIX had an "early swap allocation strategy", that means that as a program got started the page necessary to swap it out was allocated even if it was held in memory. That meant that usage rates of 60% or more weren't that troublesome at all because "swapspace used" was meaning "swapspace marked in use for eventually swapping out something now in memory". Only vmtstat could tell you the real state of the machine.

With AIX 4.3.3 ML10 that changed to a "late swap allocation strategy", like the othere major UNIX vendors employed. Swapspace is now allocated only as it is (really) needed, meaning, when processes are being swapped out of memory.

In short: without knowing which AIX version you are talking of it is simply impossible to find out what is going on on your machine.

bakunin
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