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From János Löbb <janos.l...@yale.edu>
Subject Re: very slow class loading on initial JSP/servlet request after restart
Date Tue, 24 Feb 2009 21:30:42 GMT

On Feb 24, 2009, at 4:16 PM, Sam Hokin wrote:

> Juha Laiho wrote:
>> One tool that I haven't yet seen suggested is 'strace', the Linux  
>> system
>> call tracer. This will show all the calls your application makes to  
>> the
>> operating system. As you say the application is mostly idle during  
>> the
>> delay, it is, in one way or another, waiting for some OS service to
>> complete. 'strace' should provide you with timestamped information on
>> what OS services were called, with which arguments, and how long did
>> it take for them to return with results. 'strace' will leave you with
>> a huge file (or a set of huge files, depending on the options you  
>> use),
>> and going through them will take some time - but you'll most likely
>> also find what causes the delay.
>
> Thanks, Juha.  Actually Pieter suggested it a little while ago, and  
> I've been trying to get some information out of strace.  The best I  
> can do is to put strace in front of the java command that's inside  
> catalina.sh.  That's the command that shows with ps -ef when Tomcat  
> is running.  BUT, I get nothing out of strace when I make page  
> requests on a site, it just shows output during Tomcat startup.  So,  
> I've not figured out how to get strace to say what the JVM is during  
> the delay.  jstack has led us to a stalled File.exists() in one  
> case, but we don't know what file it's looking for.  And I'm not  
> convinced that File.exists() is the only method that's stalling.
>
> Since this problem exists only on a production server, a server on  
> which I must still serve at least two customer sites (due to DNS  
> issues) in addition to our own and any others I put on there, I'm a  
> bit restricted in terms of how much I can muck with it (not that I  
> haven't brought those live sites down for awkward periods of time  
> with the diagnosis I've attempted so far).  I wish I had a test  
> environment on another server that replicates this issue, but my  
> other two servers run Tomcat perfectly fast, and since I don't  
> understand what's causing the problem, I cannot make one of my other  
> servers reproduce it.
>
> Another diagnostic problem is that undeploying a context with the  
> Tomcat /manager app, and then starting it again, does NOT reset this  
> problem - the response to a JSP request is immediate (provided it  
> had been requested since the last Tomcat startup).  This problem is  
> only reset on a given JSP if I restart Tomcat entirely; I can  
> reproduce it by creating fresh JSPs with new names and requesting  
> them.
>
> But, clearly, the key diagnostic issue is finding out WHAT is going  
> on during the delay that a JSP incurs when it is first requested of  
> a given Tomcat instance.  I've not been able to find out from  
> strace.  I'll give truss -f and truss -ff a try.
>

How about just using tcpdump during the long delay and see what the  
machine is doing network wise ?

man tcpdump

János
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