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Date: Sun, 20 Jan 2008 15:45:58 -0500 (EST)
Subject: Re: Tomcat App becomes Unresponsive
From: "tc" <tc@summerhost.net>
To: "Tomcat Users List" <users@tomcat.apache.org>
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Okay, sounds good.  Thanks.  Now if I could just figure out how to cause
it to happen...

> If you are on a UNIX jvm, issue a signal 3 (SIGQUIT) to the jvm process
> when tomcat stops responding. It will dump on standard-out (normaly
> redirected to catalina.out) the list of Threads with a stacktrace for
> each. By invstigating stacktrace you will get clues as where the problem
> is. I don't know if mysql is protected against deadlocks, but it may be
> user1 locks ressource X, user2 locks ressource Y, user1 wait for Y to
> free, user2 wait for X to free, all other users are waiting for X to
> free, filling in the ThreadQueue, tomcat then look like unresponsive.
>
> Of course the same kind of concurrency issue can occurs with
> synchronized{} blocks
>
> Note, you can also get such dump on windows, it requires you to press
> magic key combinaison in JVM terminal (don't remember which)
> tc a �crit :
>> I have been asked to investigate a tomcat/java application.
>>
>> The basic problem is that this application sometimes becomes
>> unresponsive
>> if more than one user uses it at a time.  Restarting Tomcat clears the
>> problem.  I don't think it has ever occurred when only one person was
>> using the app.
>>
>> It is a fairly straight forward data-entry app; the data is stored in a
>> mysql database.
>>
>> The developers think there may some issue with the database.  They have
>> also done multi-user testing without being able to reproduce the
>> problem.
>>
>> I'm looking for pointers to any resources on the web or elsewhere that
>> can
>> help me track down the problem, or ideas about where to look, or what we
>> can do to improve post-freeze diagnosis of this problem.
>>
>> I am also a developer, but I don't have a lot of experience with Java or
>> Tomcat.  I'm trying to bring a fresh perspective to this problem.
>>
>> Thanks.
>>
>>
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