Memory upgrade and swap partition size

[Jon maddog Hall]

Kjel,

kjel.anderson at gmail.com said:
> I am probably exposing my ignorance by asking this, but I have to remember:
> there are no stupid questions, just stupid people. 

This is not a stupid question.  Increasing SWAP size on your disk will not generally
improve performance.  SWAP size increases will allow you to run more programs
simultaneously or programs with with larger datasets, but the things related to
"SWAP" that will generally give you better PERFORMANCE are:

o RAID striping of your SWAP partition
o placement of SWAP on a seldom used disk spindle (same thing with /tmp and /usr/tmp)
o allocation and placement of multiple swap partitions to minimize disk latencies
o having more RAM (always more RAM)
o Solid state SWAP devices

SWAP is used in two instances:

	o you have more data than you have RAM memory (text is paged out of the
	  text files, not out of SWAP)
	o after a certain period of inactivity, processes are "swapped" out to SWAP
	  to make room for the more active processes

These are general rules of thumb.

If your SWAP is not large enough, you will get fairly obvious error messages telling
you that you are in that situation.

Disk space is cheap these days, and I normally have a gig of swap space
on my notebook, along with the two gigs of memory I have.  I can not remember the
last time I ran out of "swap" space, if ever.  On the other hand, if you are running
a large server with a large database, you might indeed run out of "swap" at some time.

There are tuning parameters inside of the kernel that control SWAP, when it takes over,
how much RAM is reserved for things like buffer cache and other forms of memory
management, but this is probably more than you want to know or fiddle with.....trust
me.

md
-- 
Jon "maddog" Hall
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