Jerry McAllister wrote:

On Thu, Nov 09, 2006 at 05:26:38PM +0000, Alex Zbyslaw wrote:

Jerry McAllister wrote:

On Thu, Nov 09, 2006 at 06:39:50AM +0100, VeeJay wrote:

Maximum space required for SWAP to get high performance.
If you end up using swap space you will *not* get performance. The second you start swapping is the second that your performance goes into a downward spiral, especially with multi-user servers.

Sort of, but don't forget paging.
The system always pages - pushes out pages that don't get used
so often, but are still part of the active processes.   The
system pages to swap space.    Paging and possible core dumps
are the main uses of swap space, not actual swapping.

Sure. I should probably have said "If you end up using swap space for swapping ..."

I wasn't advocating not having any swap space, just pointing out that maximizing swap space in no way maximized performance of a multi-user server, just made it's death from overwork that much more drawn out. There are certainly uses for swap space, but generally the least desirable usage is swapping. Maximizing swap space won't improve any paging usage, though splitting it across multiple disks might, and once you get a core dump you don't exactly have maximum performance either ;-)

Personally I still go by the hoary old rule of thumb - 2x RAM, or even 4x RAM to allow for possible upgrades. But if I actually used it for swapping on a regular basis I'd be looking at the price of larger memory sticks - or writing the software more efficiently :-)


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