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From André Warnier>
Subject Re: what is it doing ?
Date Tue, 19 Oct 2010 16:51:31 GMT
Justin Randall wrote:
> Hello,
>>>From a general Linux perspective, if you have a knowledge of Linux system calls,

not really

>> along with what operations are performed by which web application 

not really either.  Basically, that is what I am trying to find out.

(One might wonder what I really do know, I know. My colleagues also wonder.)

I see (with top) that Tomcat as a process is busy doing something, but what I don't know 
is what within Tomcat is doing it.
This Tomcat runs a number of webapps, a minority of which I really have an idea of what 
they are supposed to be doing.  And precisely these should not be doing anything at the 
times I'm watching.  So my suspicion is one of the others, but I may be wrong, and that's

what I am trying to figure out.

you could use "strace" (use the -f to follow threads).  Depending on what you're 
interested in you can filter further for operations on files or network activity (i.e. "-e

trace=file,network,desc").  If you see a lot of erroneous activity (such as constantly 
trying to open/stat a file that doesn't exist) and you know which web app (or Tomcat) is 
responsible you can address the issue.
> You could also check "top" to see whether the CPU is being consumed in usr or sys space,
along with whether maybe the memory on your system is maxed out (trigger high CPU load transfer
data between RAM and swap space).

There may be that too, but at this point I believe not.  "top" and "free", each time I 
look, show the swap space to be virtually unused.
The system as a whole is not overloaded, and the Tomcat-centric CPU usage, although high 
in percentage, is finally a percentage of not very much.
Let's just say that I am curious, apart from the fact that some Tomcat applications which

should answer quickly don't always.

So it's the thread dumps route for me then I guess ?
I was hoping someone would just point me to this nice "java-top" Debian package...

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