topic Re: Swap Question in Operating System - HP-UX

Swap Question

Dwayne De Salvo — Mon, 13 Mar 2006 17:36:02 GMT

I have an existing swap space at 4000mb. I needed an 8000mb swap for oracle, so I created an additional 8000mb swap. My question is, if I were to reduce the 8000mb swap to 4000mb, would oracle use both equally when needed, and would there be any loss of performance doing so?

Re: Swap Question

A. Clay Stephenson — Mon, 13 Mar 2006 17:42:37 GMT

The system allocates swap usage based upon the priority; e.g. all swap at priority 1 will be used before any at priority 2; all priority 2 will used before any at priority 3; and so on. Primary swap is set to priority 1 but you can define additional swap at 1 as well. When multiple swap devices are found at equal priority, swap usage is interleaved among them.

In you case, if your 4000 and 8000 MB swap were left at that size and the priorities are equal. Then the usage would be interleaved until 4000MB on the two swap devices were used. Additional swap would have to be drawn from the remaining area on the 8000MB area.

Now having said all this, it really doesn't matter. The performance impact from swapping is so great that worrying about swap layout is like rearranging the deck chairs on the Titanic.

Re: Swap Question

TwoProc — Mon, 13 Mar 2006 17:48:21 GMT

You can run with two 4000's fine. Whether or not you interleave them with their priorities (re: SEP post above), is up to you, but at the point at which you're ACTUALLY swapping, both your users and your Oracle server are in the drink anyways. Make sure you've got your system ram and Oracle configured NOT TO GO INTO SWAP, ever, and whether or not you interleave swap will never be noticed. If you do go into swap, your system will run like a slug regardless of how slick you set up swap.

Re: Swap Question

TwoProc — Mon, 13 Mar 2006 17:57:19 GMT

Whoops, reference to "above" was A. Clay's not SEPs. Sorry Clay.

Re: Swap Question

A. Clay Stephenson — Mon, 13 Mar 2006 20:58:30 GMT

Oh, it is dumb to have multiple swap areas of equal priority on the same physical disk because the interleaving will cause excessive head movement but, once again, it's rearranging the Titanic's deck chairs -- so that really doesn't matter either.

Re: Swap Question

Stanimir — Wed, 15 Mar 2006 09:52:01 GMT

It seems you will not have any problems and losing of performance in this situation..

Re: Swap Question

Carlos Roberto Schimidt — Wed, 15 Mar 2006 14:07:04 GMT

Hi,

If you reduce with equal priority, yes.

But is better if new swap device belong to diferent disk for perfomance and avoid I/O contetion.

Schimidt

Re: Swap Question

Kent Ostby — Wed, 15 Mar 2006 14:09:49 GMT

The other part of the equation is to make sure that you've got at least 2x device swap per RAM (so 2 gig of RAM translates to a minimum of 4 gig of device swap).

Re: Swap Question

Carlos Roberto Schimidt — Wed, 15 Mar 2006 14:38:25 GMT

If you have pseudo swap enable, its not necessaary have many space swap.