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From André Warnier ...@ice-sa.com>
Subject Re: Simple Tomcat monitoring ?
Date Tue, 12 Apr 2011 12:18:25 GMT
Borut Hadžialić wrote:
> I'm gonna try to make a guess here :)
> 
>> top - 08:20:02 up 72 days,  9:39,  4 users,  load average: 6.83, 5.63, 3.16
>> Tasks: 265 total,   1 running, 264 sleeping,   0 stopped,   0 zombie
>> Cpu(s):  0.2%us,  0.1%sy,  0.0%ni, 99.2%id,  0.5%wa,  0.0%hi,  0.0%si,  0.0%st
>> Mem:  12328624k total, 11382976k used,   945648k free,   123400k buffers
>> Swap:  4882424k total,      860k used,  4881564k free,  7565012k cached
> 
> - somewhat large load average (6.83)
> - but no io waiting (0.5%wa),
> - app is heavily used
> - tomcat requests take long time (sometimes takes few seconds to
> produce the answer).
> 
> Could it be a lack of threads at apache or tomcat?

Spot on for the observation.

That is one of the things that puzzle me : overall CPU usage is very low, and there is no

i/o wait.  Yet the load average is high (which should mean that a number of processes are

constantly waiting for something), and Tomcat is using 333% of CPU time (which may be very

little time in an absolute sense, but is puzzling anyway).
And the clients are waiting.
So where are the time/resources being spent ?

About threads :
- Apache (prefork) MaxClients is set to 150
- Tomcat AJP Connector does not specify any thread parameters, so defaults apply, which 
should be :
maxThreads : 200
maxSpareThreads : 50	
minSpareThreads : 4	

Considering that Apache handles most requests for static contents, I think that the 
numbers should be about right.
But not having so far done any real monitoring, that may be wrong.  Which is one of the 
things I'd like to check.

I think I'll start by making the Tomcat AJP Connector parameters explicit, and raise the 
minSpareThreads a bit.  And also its Heap size.
But I don't like to start changing things left and right, without knowing exactly why I'm

doing it.

Is there for example any parameter or command-line switch that I can use for the JVM or 
Tomcat, which would tell me a bit more (in the logs) about when Tomcat is starting a new 
thread, how many are alive on average etc.. ?



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