Swap Question

[Dwayne De Salvo]

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?

[A. Clay Stephenson]

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.

[TwoProc]

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.

[TwoProc]

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

[A. Clay Stephenson]

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.

[Stanimir]

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

[Carlos Roberto Schimidt]

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

[Kent Ostby]

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).

[Carlos Roberto Schimidt]

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