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Tomcat has got that well-known memory leak problem that causes PermGen space errors after too much redeploying.

What I'd like to know is best practices to reload the server in a way that completely resets that space and erases existing memory leaks. Just using shutdown.sh and startup.sh isn't cutting it: it seems that leaked memory stays leaked. Rebooting the machine works of course, but I'd like to know if a quicker/cleaner/safer solution exists.

Thanks!

(I can allocate more PermGen space, of course, but that's just delaying the problem, and I'd like to flush away the leaked memory before I declare the apps as production-ready, since I'm changing jobs afterwards and thus the apps won't get redeployed for a while)

EDIT: as mentioned in the comments below, it seems the scripts are supposed to flush all memory already since they create a new JVM, so there must be some other factor causing PermGen errors to keep happening even in a new JVM, after many redeploys.

userBigNum
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    shutdown.sh and startup.sh will always work to free all memory. It will kill the JVM and create a new one in a new process. It's not possible that a memory leak is transferred from one JVM to another one. – Codo Jul 03 '12 at 14:21
  • Hmm could the kill not be working or something? Because I've had this kind of issue a few times already. Maybe even if the JVM is killed, Tomcat's memory usage rate ramps up on redeploys, and that rate isn't reset even on a new JVM? Only way I can imagine that happening is if there's something happening on disk, weird... I'll edit the question, thanks man. – userBigNum Jul 03 '12 at 15:05
  • Could the leak be caused by something stored in the sessions ? Tomcat can persist sessions on disk and restore them after restart. Just a guess. – David Levesque Jul 03 '12 at 15:35
  • Good call, that'll have to be my guess too. I'm using a framework that's particularly heavy session-wise, so I'll do some in-depth profiling and try to confirm if that could be the cause. Thanks. – userBigNum Jul 04 '12 at 11:12

3 Answers3

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Tomcat does not have PermGen leaks, webapp redeploys or not. The problem is either with your webapp itself, a library you use, or, in some cases, the Java standard library implementation. All of these can be solved without resorting to throwing up your arms and blaming Tomcat.

Try reading http://people.apache.org/~markt/presentations/2010-11-04-Memory-Leaks-60mins.pdf to learn how to diagnose these leaks properly. Get yourself a profiler (this can even be done with freely-available utilities included in the JDK like JVisualVM).

Tomcat 7 includes a memory leak prevention utility that can work-around problematic Java API implementations (e.g. AWT). Everything else is your problem or your libraries' problems. Most open-source libraries where such PermGen leaks have been found have quickly worked to patch their libraries in order to avoid them (or provide a graceful way for client code to avoid a PermGen leak).

Christopher Schultz
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In case you haven't solved this problem yet, you can try Plumbr. Just released version has a PermGen monitoring capability as well.

Nikem
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  • Well, it's working fine after a few server restarts, but I'll take a look into Plumbr, sounds really useful. – userBigNum Jul 12 '12 at 13:00
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This script will automatically restart the Tomcat server instance when it exceeds 95% of physical memory. Enjoy!

porcentaje=95
usoMemoria=$(ps aux | grep tomcat | grep -v grep | awk '{printf ("%.0f", $4)}')
if [ $usoMemoria -ge $porcentaje ]; then
  echo "Se ha superado el tope (95%) de memoria que se ha establecido para el Tomcat. Se procede a su reinicio automatico"
  echo "$(date)"
  echo "Comenzando..."
  service tomcat7 restart
  echo "Terminando Script..."
fi
exit 0
Ryan Ransford
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