Primary Swap Advice Needed

[Brando Sumayao]

What is the problem if the primary swap is higher than 512mb?

Oracle install for 8.1.7 recommends at least 3 times the size of the physical mem (in my case, it is 256 mb), so I am looking 768mb.

Got this warning from our "guru" Bill McNamara.

Thank.

Brando

[harry d brown jr]

Nothing. Typically I make primary swap 2 times memory, but with a strict sense of how much memory I have. For example if I have 12 GB of memory I am not gouing to make a swap space 24GB. I won't even make it 12GB, usually not larger than 6gb.


live free or die
harry

[S.K. Chan]

In your case since your physical meory is only 256MB it's perfectly alright to have swap three times it's size. I would break it up into 2 or 3 device swaps not just having one single primary swap. If your physical memory is large (in GBs), psuedo swap will come in play and you would want to pur some effort in calculation how much swap your application needs.

[Jim Turner]

Hi Brando,

If you increase swap beyond what your current kernel can handle, you'll need to increase "maxswapchunks" accordingly.

My general disdain for Oracle's viral-like resource thirst notwithstanding, you can set up as much swap as you like. Here's my little recommendation: Leave your vg00 swap alone. It's probably 512M or 1G at priority 1. What you need to do is create your additional swap striped across as many of the fastest disks you've got and set it at priority 0. This will ensure the least performance hit in the (undesirable) event you have to start actively using swap (vice zero-cost swap reservation).

Keep in mind that you do pay a horrible price for actively using swap on a routine basis. In such a case, adding RAM is a real requirement -- unless, of course, you enjoy getting repeated calls from users pissing and moaning about performance.

All the best!
Jim

Small memory models and Oracle do not mix.
Like calculus: Don't drink and derive.

[A. Clay Stephenson]

Hi:

With only 256 MB on Oracle 8.1.7, chances are that you will be swapping and possibly more than you want to. In that case, if you can, configure at least 2 separate physical devices for swapping. I actually would prefer to make primary swap as small as possible (it gets prioirity 1) and then have 2 other devices
set at priority 0. The idea is that the swapping occurs on the non-vg00 disks (vg00 disks are already busy) and by setting them at equal priority (0), the swapping load is interleaved between them. Only when the 0 priority swap space is used up does the primary swap space get hit.

Normally, I get a machine with enough memory so that I never swap. I configure no more than 256 MB of primary swap, turn pseudo-swap on, and then to feel safe I create filesystem swap at very low (high number) priority. But if you can't afford to buy that much memory, the interleaved device swap is the next less evil choice.