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From Marcus Crafter <craft...@osa.de>
Subject Re: LoadTest
Date Tue, 21 Aug 2001 23:32:22 GMT
Hi All,

	We've also been experiencing such problems for the last 2 weeks or so,
	mainly a decrease in performance/response over time under reasonable
	load.

	We had a range of errors:

	o components not found: fixed recently in avalon's DefaultPool
	  (also seems to have improved what was before a memory leak)
	
	o multiple sitemap recompilations: fixed recently under article
	  'sitemap creation threading issue'
	
	o decreased performance over time (100 users lasts about 20 minutes,
	  50 users lasts about 40 minutes with our application, before
	  performance drops)
	
	We've been using an up-to-date version of Cocoon2 from trunk CVS and
	have been following the discussions on the mailing list very closely.

	In our situation, we've noticed that under load the application's
	performance and response time decreases dramatically, however the
	machine does recover after load has dropped. Once load drops, the
	application starts to settle down and returns to a normal state
	operating state.

	During times of poor performance/response time however, our
	application server is *not* out of resources. We've been able to
	ascertain that both memory and CPU resources are available.

	What could cause such a phenomenon ?

	Memory leaks ? I'm not sure if a memory leak would cause a drop in
	performance, unless excessive garbage collection was being done (but
	we have 2gig of RAM, of which 800 meg is not even touched)

	Runaway threads ? Could cause such a problem, but they wouldn't allow
	the system to regain itself - or should I not assume this ?

	Synchronization problems ? Could there be some synchronization issues
	there which force the jvm to queue threads up for entry to a
	particular method/code block which is considered to be a critical
	area ?

	Threading issues ? We've also seen cases in the log files under load
	where a single (same) request is handled by 4 separate threads, all
	starting in the same second - quite vexing.
	
	Our environment is a on a Sun Enterprise 250 (2x450mhz UltraII, 2gig
	ram), with Tomcat 3.2.3, CVS Cocoon2, and our reporting application
	(generates various html tables and pdf reports).

	If you have any comments, or questions regarding what we've seen,
	please feel free to respond.

	Cheers,

	Marcus

> Hi all, 
> 
> I'm back from the dungeons of load testing. And I don't have particularly
> good news, I'm afraid.
> 
> C2 leaks memory and CPU. The accompanying PNG shows the graphs of a loadtest
> with loadrunner, on tomcat 3.2.1 and C2 cvs version of last week, with 50
> concurrent users surfing around on the simple sample pages (no xsp, no sql,
> just the xml->html pages)
> 
> The graphs don't look good, to say the least. 
> 
> Moreover, when I stopped loadrunner, and monitored the CPU used by java, it
> kept burning 50-70% (even after 2 days). It was sort of cyclic behaviour: it
> dropped to 0%, raised to 50-70%, dropped again to 0%, and so on. I also saw
> the java process eating memory away (approx. 10MB/h)
> 
> The test was done with loadrunner 6.5 on a single 350 MHz cpu with 196MB
> RAM, OS: NT 4, JVM: Sun JDK1.3.1.
> 
> And now for the really bad news: I don't have a clue as how to find the
> source of such a leak. I could browse step-by-step through the code, but
> this seems a daunting task to say the least. Has anyone some hints as to say
> "I would begin looking there", or "I would first test this and see what
> happens", ... ? I've already been musing about the pooling of the components
> (probably components that aren't given back to the pool), but that is also
> pretty hard to find.
> 
> Thanks for any pointers,
> 
> tomK
 
-- 
        .....
     ,,$$$$$$$$$,      Marcus Crafter
    ;$'      '$$$$:    Computer Systems Engineer
    $:         $$$$:   Open Software Associates GmbH
     $       o_)$$$:   82-84 Mainzer Landstrasse
     ;$,    _/\ &&:'   60327 Frankfurt Germany
       '     /( &&&
           \_&&&&'     Email : Marcus.Crafter@osa.de
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