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From Aidan Fitzpatrick <aidan.fitzpatr...@zdnet.co.uk>
Subject Tomcat 3 serving wrong pages under load?
Date Thu, 23 May 2002 20:49:12 GMT

What's my problem?

I'm encountering a problem with Tomcat 3 that I'm finding quite hard to describe and search
for succinctly. I'll outline it below, in the hope that someone on the list can point me in
the right direction. I'll assemble some more information and raise a bug if that's the case.

I've got a web application running under 3.3a that is running under a fairly low load of around
five pages per second. (There's a mechanism which sits on top of this to cache the output
of the pages, so this load is irregular.) When Tomcat is receiving these concurrent requests,
the pages it serves are occasionally incorrect. The higher the load I put it under -- up to
ten concurrent requests at any one time for a prolonged period -- the less accurate it's responses
are.

For instance:
	http://servername/contextname/servletname?argument=1

...will not always return me the same page. If the webapp is being loaded with requests for
argument=2, or argument=3, I might get one of those instead.

What have I done about it?

Very little so far, as it's taken me a while to isolate the problem to this level. I've not
been able to find any other report of this problem on the 'net, so I'll be looking further
into my application. I've tried turning most of the pooling and caching off, and I'll ensure
I get it all off. I'll try to provide a demonstrable test-case, and I'll also look towards
testing this on Tomcat 4, too, if no one tells me I'm wildly off-course.

What do I think it could be?

I've replicated the problem with Apache 1.3.22 using the mod_jk that comes with 3.3a, and
also directly with Tomcat. I believe it could be:

* My worker configuration. (I can't imagine it's not thread-safe. I've not changed it from
the default.)
* My web application. (I think this is unlikely, but I would say that! :) )
* Tomcat 3.

I've seen this behaviour under Linux and Solaris 2.6 and 5.8. I've also seen it with Tomcat
3.2.1.

Any pointers would be very appreciated!

Aidan Fitzpatrick

--

Aidan Fitzpatrick, Software Engineer, EU Tech Team
Tel: +44 (0) 207 903 6074 Fax: +44 (0) 207 903 6000 YIM: aidan_fitzpatrick
ZDNet, International House, 1 St. Katharine's Way, London, E1W 1UN

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