posted by mthomas on March 28, 2013 06:33 AM

It is late on a Friday afternoon, and your web application has stopped responding to requests. The server is still reachable, and the Apache Tomcat process is still running–there are no errors in the logs. You want to go home but you can’t until it is fixed. What do you do?

If your answer is “restart Tomcat and hope it stays up until Monday,” then this article is for you.

Rather than keeping your fingers crossed and hoping you don’t get an angry call from your boss over the weekend, this article will provide you with some simple steps you can take to diagnose the problem. 

Step 1: What is Tomcat Doing? Thread Dumps Begin to Answer the Question

If the Tomcat process is running, then it must be doing something. The question is what is it doing when it should be responding to requests? The way to answer that question is with a thread dump–actually, a series of thread dumps. You need to take three thread dumps roughly 10 seconds apart and then compare them. I always compare them with a diff tool rather than by eye—a it is far too easy to miss subtle but important differences between the dumps.

How you generate a thread dump depends on your operating system and how you are running Tomcat. On Linux, FreeBSD, Solaris etc. use kill -3 to trigger a thread dump. On Windows use CTRL-BREAK if Tomcat is running in a console window. If Tomcat is running as a service, then the service wrapper should provide a way to trigger a thread dump. Commons Daemon (the service wrapper that ships with Tomcat) provides an option to trigger a thread dump via the system tray icon.

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posted by mthomas on February 28, 2013 10:19 AM

ApacheCon North America is almost concluding, and my experience this year has not disappointed. It’s been great to be able to meet up with lots of other project committers. Many committers make the trek to ApacheCon wherever it is in the world and, given that we normally work together just via the project mailing lists, it has been great to be able to discuss current issues and new ideas face to face. Of course, all of these discussions will be making their way (if they aren't there already) to the Tomcat dev mailing list so the everyone in the community can participate.

Personally, I have spent a great deal of my time in presentations. I have spoken about progress on Tomcat 8, delivered another session on clustering and two on security covering vulnerabilities and security response at the ASF. As always, slides are available from http://people.apache.org/~markt and there should be video and audio recordings available as well at some point. Most sessions were reasonably well attended and the conversation and questions flowed after the presentations. Here are some of the questions and answers I found most interesting:

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