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From Berin Loritsch <blorit...@apache.org>
Subject Re: Strange problems with concurrent access of Xalan-2.0.0
Date Fri, 16 Feb 2001 13:32:59 GMT
Giacomo Pati wrote:
> 
> Berin Loritsch wrote:
> > Giacomo Pati wrote:
> > > Carsten Ziegeler wrote:
> > > > Hello,
> > > >
> > > > since the switch from the Xalan2D07 to the Xalan-2.0.0 version in
> > > > Cocoon2 we get sometimes very strange problems.
> > > >
> > > > We are using frames which all four use the same stylesheets. The xalan
> > > > is driven by the cocoon pipeline.
> > > >
> > > > If we turn on the storing (formerly known as caching) of the
> > > > TraxTransformer we get from time to time a NPE in one frame. Sometimes
> > > > its even worse: One frame contains part of the content of another frame
> > > > and the other frame is totally broken. Reloading the whole page brings
> > > > up all frames correctly.
> > > >
> > > > However if we turn off the storing we never did see this phenomenen. So
> > > > we assume that this problems have something to do with the storing.
> > > >
> > > > The store stores the Templates. Is it possible, that this problem can
> > > > occure, when several threads use the same Template (as delivered by the
> > > > store). A thread might finish first, resetting the template and the
> > > > other thread still try to use it.
> > >
> > > A Template IIRC should be thread safe but the actual transformation is
> > > done by a Transformer object which can be obtained from the Template (or
> > > is it the other way around?).
> > >
> > > Wait a second I'll try to do a stress test using ab....
> > >
> > >     ab -c 20 -n 200 http://localhost:8080/cocoon/welcome
> > >
> > > No, I can't reproduce the failure. All runs well here.
> > >
> > > Any guesses from the Xalan Team?
> > >
> > > Giacomo
> >
> > I ran accross this abnormality when I stress tested Cocoon using
> > Apache JRun.  Please note, that I had to have the requests comming
> > _very_ quickly to to actually get it to show up.
> 
> What is Apache JRun? The ab command I've use above uses 20 concurrent threads
> pounding a total of 200 requests on to a Tomcat 3.2.1 and the latest C2. Did
> you add more concurrent requests?
> 
> Giacomo

Ooops, I meant Apache JMeter--I have been discussing alternative Application
Servers with people at my job, My brain farted on me.

I had 20 threads pounding every 300 ms +/- 300 ms with a gaussian dispersion
on the deviation.  I actually got this running JMeter with 12 concurrent
threads every 1000 ms +/- 1000 ms with gaussian dispersion on deviation.
Note, that it was only once or twice.  I didn't think too much of it because
the webapp we are designing won't be seeing that much activity.  Note the
12 thread scenario corresponds to 1,036,800 page requests a day spread
evenly throughout the day.

I ran the test for ~20-30 seconds.  It happened early in the test, but it
didn't happen again after that.

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