Tuning Question

Lowell Gilbert freebsd-questions-local at be-well.ilk.org
Mon Feb 12 15:50:30 UTC 2007

Cy Schubert <Cy.Schubert at komquats.com> writes:

> Top's output, as is free memory on all O/S's these days, is bogus. It's the 
> size of the free memory pool which is available for immediate allocation. 
> Used memory is just as  useless. It doesn't matter how much is swapped out, 
> what matters is how much I/O is being performed to support VM. I know at 
> work, which is an Oracle ghetto, paging should be kept at a minimum, 
> especially the SGA. Other apps can afford more. In the case of an average 
> FreeBSD system it's been guesswork.

What I thought you should use top for is tracking the swapping
rates.  But that's not enough, because the acceptable rates will
depend on what else is happening in the system.  If the CPU is maxed
out anyway (for example), then reducing the swapping will not
improve your performance.

My general approach to optimization is to identify a problem first.
If you can't pin down a performance problem that you want to solve,
then you aren't going to be able to prove that any changes fix that
problem anyway.

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