On Tue, 13 Feb 2001, Reynald I. Ngo wrote:
..
> Some says that for a typical server... you need to double your
> physical memory for swap. If your linux box will be a database server...
> you need to triple your physical memory for swap. I dunno... just an
> advice of my former boss. {=)
..
in this day and age, that info is wrong.
first, the 2x physical memory or 3x physical memory is good advice for
BSD-derived boxen, or solaris2. this is because these OS'es store the
decoded executsble images in swap for fast reloading (e.g. after loading
the ELF or A.OUT executable, after exiting, the in-core image is saved to
swap so that next time, it doesn't have to be decoded).
since linux doesn't do that, linux has much smaller swap usage than these
others.
second, have you actually had a database server that was heavily
swapping? i cringe to think of the performance loss. oracle's docs plainly
state that your your SGA should be at most 1/3rd of physical memory to
avoid swapping, because swapping will kill your performance. so, even
though lots of swap may seem prudent, in reality you dont ever want to
touch that swap..
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