i moved away from Red Hat 2.4x kernels as they have an annoying tendency
to swap instead of giving back cache. I moved to Centos-4 and i have
vm.swappiness to zero and am using at most 144K of swap across 5 machines.
John Summerfield wrote:
hkclark@xxxxxxxxx wrote:
On 2/9/07, Vasiliy Boulytchev <vasiliy@xxxxxxxxxxxxxxxx> wrote:
Gents, am I reading this information incorrectly, or is this box also
swapping about 128M? Swapping will quickly grind your system to a halt.
I guess this all depends on how many people are connecting to your
apache servers... Turn on your server-info and see :)
Vasiliy Boulytchev
vasiliy@xxxxxxxxxxxxxxxx
Hmmm, now that you mention it, that's a very good point. Does anyone
out there know why CentOS 3 would swap out so much vs. "giving back
real RAM" from buffers and/or cache? I agree with Vasiliy that it
looks like the performance on this box could be pretty lame if
anything important is in that swap (I would assume the OS is putting
the "oldest" stuff in swap, but what if an app didn't need to get used
very often and it suddenly received a request... that request could
easily time out while stuff is swapping back in from disk, right?).
Does anyone know a good way to see which app(s) and/or parts of the
OS/libs are being put into swap vs. kept in "real RAM"?
I haven't seen anything like the correct answer yet; as always, it's "It
depends."
What applications are running, and what are they doing?
The RAM used by the OS itself is overhead, pure and simple. The
important RAM is what's being used to process the workload.
If you're using mysql, postgresql, Apache, those are all using RAM, and
the new versions may use more:-)
Or less, depending.
The new version of Perl could have some impact too, and the new
application certainly will. So will increasing business.
I don't want the answers to those qs, but you need them (and probably
more besides). Then analyse the data and draw conclusions.
Or just, "Stuff it, we'll do it and fix it later." This may be the
cheapest.
--
My "Foundation" verse:
Isa 54:17 No weapon that is formed against thee shall prosper; and
every tongue that shall rise against thee in judgment thou shalt
condemn. This is the heritage of the servants of the LORD, and their
righteousness is of me, saith the LORD.
-- carpe ductum -- "Grab the tape"
CDTT (Certified Duct Tape Technician)
Linux user #322099
Machines:
206822
256638
276825
http://counter.li.org/
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