Virtual Memory Settings for 64 bit Unix boxes

Question

I am running out of virtual memory on my Unix box. I have several applications running, including ASO cubes. My config is as follows:
8 Gig Ram
16 Gig Virtual
Solaris 10-64
Essbase 9.3.1 64 bit
Can I set my virtual ram higher or do I need to bump up my physical ram first?

Answer 1

The goal of having virtual memory is not to increase native capacity, but to provide a place for inactive tasks to be "nearly" active.
It is the things you list which make it possible (although admitedly not likely) that a decrease can improve performance. Virtual memory is much slower than real memory, and this is even more of a problem when you have to exchange larger amounts than needed.
The extra page thrashing may occur simply because one program uses memory voraciously when it could otherwise do with less. It could selfishly improve it's performance by 10% by using twice the memory it needs, while causing the system to do everything else through virtual memory. Prior to 64 bit, Essbase would only see 2 GB and thrashing would be a small incremental issue. Now each app can do 4+ times the thrashing as they swap each other out, using significantly more memory to gain a relatively small gain, and grinding the system (as a system) to a halt. Every time the programs switch, the same extra large thrashing is repeated to make room for that voracious appitite again.
Thus the performance issue can occur not so much because there is too little left over, but too much being swapped in between. Both applications may very well work better if they starved a little bit and did more thrashing on smaller work files at slightly less individual performance. This is because they could potentially get the job done with less memory but over-reached as a result of seeing an abundance.
This is a situational condition though, due in part from using software that is aggressive by nature and an OS that supports a lot more memory than previously.
That said, it is still more likely that the answer is to either cut back on memory usage or to add more real memory. If you can reconfigure the individual applications to use less overall, great -- if you can't, add more real memory.
BTW: I've never had issues with Unix based OS's virtual memory -- but my only experience was AIX and I didn't have to deal with hardware on that gig.
Still, I'd recommend that if you can't put your apps on a diet, you test with 12, 16, and 20 GB of virtual memory to find which direction helps, then add real memory if additional virtual memory really helps much.