[CentOS] CentOS 3 vs. CentOS 4 Memory Utilization

[John Summerfield]

hkclark at gmail.com wrote:
> On 2/9/07, Vasiliy Boulytchev <vasiliy at linuxspecial.com> 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 at linuxspecial.com
>>
> 
> 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.



-- 

Cheers
John

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