Re: [squid-users] Squid slowness over time ...

Checking memory usage is a general Unix skill. You'll want to grab a
good Unix system administration book, before getting yourself too deeply
into any specific applications for your Unix server (a good start is
Essential System Administration by Frisch).

But in this case, try the manpage for top:

man top

Your primary concern is whether Squid has partially swapped out due to
its size. For an example, the memory section on my workstation looks
like this at the moment:

Mem: 385028K av, 352000K used, 33028K free, 0K shrd, 24824K buff
Swap: 535096K av, 145856K used, 389240K free 143476K cached

Here I have 33MB of free memory, 145MB in Swap, and 24MB + 143MB used
for buffer/cache. It is safe to think of buffer/cache as being 'free'
as it is always available for the OS to use without requiring anything
to be swapped out. So my total available memory at this moment is about
200MB out of 384MB.

On a dedicated Squid box, if you see /any/ swap usage over about 15MB
you have a problem (like not enough memory). If the box is a shared
machine that does multiple tasks, then swap usage may or may not be a
problem (but probably is). In my example case, this is a desktop
machine where there are lots of idle processes that just sit and rarely
are called upon to do anything (print server, test webserver, lots idle
shells, etc.) and so they get swapped out. Squid, if it ever gets even
partly swapped out, it will severely impact performance since it has to
be swapped back in before it can answer a request.

This is all pretty simplified, but ought to at least allow you to look
at your memory usage well enough to know if that is your problem (it
probably is...the problem of not enough memory for Squid is so common
that it has a gigantic section in the FAQ, and we still get memory
questions several times a week).

It is possible to make top tell you how much of a given process is
swapped out, by using the add field option of top. I'll leave the
discovery of how to use that gem as an exercise for the reader.

Justin Hennessy wrote:
> Marc,
>
> I am running RedHat 7.2.
>
> I am not confident to assess the memory usage. I have cachemgr up and
> running but am not really familiar with how to use the information.
>
> I have had a look in the cache file but I am not really sure that I am
> looking for.
>
> Justin

-- 
Joe Cooper <joe@swelltech.com>
Web caching appliances and support.
http://www.swelltech.com