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From Apache Wiki <wikidi...@apache.org>
Subject [Tomcat Wiki] Update of "FAQ/Bugs/Memory" by GianlucaVarisco
Date Wed, 28 Nov 2007 19:01:49 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Tomcat Wiki" for change notification.

The following page has been changed by GianlucaVarisco:
http://wiki.apache.org/tomcat/FAQ/Bugs/Memory

New page:
== Preface ==

This page discusses various memory issues. In a nutshell - if your computer has less than
128MB of ram - you will probably have trouble. Anyhow, also read the following threads for
other memory related issues:

 * [http://marc.theaimsgroup.com/?t=104388973000006&r=1&w=2 java.lang.OutOfMemoryError
during deploy]
 * [http://marc.theaimsgroup.com/?t=104378347700007&r=1&w=2 Memory requirements]
 * [http://marc.theaimsgroup.com/?t=104333066400004&r=1&w=2 Memory Mgmt Tomcat]
 * [http://marc.theaimsgroup.com/?t=103011379700006&r=1&w=2 Tomcat Out of memory]
 * [http://marc.theaimsgroup.com/?t=104519961700002&r=1&w=2 Tracking memory usage
over time]

Also look at [http://java.quest.com/jprobe/jprobe.shtml JProbe], or [http://www.borland.com/optimizeit/
OptimizeIt], or other profiling tools. Lots of people recommend these tools. This is not an
endorsement for them, I just notice other people like them.

=== JSP Recompilation ===
If your application uses JSPs which are frequently recompiled at runtime, e.g. headers that
change value hourly, please make sure to read the JSP HOW-TO page and RELEASE NOTES documents.
You may wish to tune the JSP compiler configuration to prevent memory leaks. Of course, these
are documents you should have read by now anyways..

== Questions ==

'''How do I adjust memory settings?'''

First look at {{{java -X}}} to determine what parameters to set. Then you can set them via
the environment variable {{{JAVA_OPTS}}}. Read the files catalina.bat or catalina.sh for more
information on JAVA_OPTS.

'''Why do I get OutOfMemoryError errors?'''

Many reasons.

 * You're out of memory. Simple as that - add more to your heap.
 * You're out of memory. You have code which is hanging onto object references and the garbage
collector can't do its job. Get a profiler to debug this one.
 * You ran out of file descriptors. If you are on a *nix system, it has been observed that
an OutOfMemoryError can be thrown if you run out of file descriptors. This can occur if your
threshold is too low. The ulimit program can help you out here. You also may need to account
for socket connections too when thinking about these thresholds. Google is your friend for
getting more information about this topic.
 * You have too many threads running. Some OS's have a limit to the number of threads which
may be executed by a single process. (Which is what the JVM is.) Refer to your OS docs for
more information on how to raise this threshold.
 * If you have a lot of servlets or JSP's, you may need to increase your permanent generation.
By default, it is 64MB. Doubling it to be {{{-XX:MaxPermSize=256m}}} might be a good start.
 * Your OS limits the amount of memory your process may take. OK, this one is grasping at
straws.
 * The JVM has a bug. This has been known to happen with JVM1.2.? and using EJB's with another
servlet engine.
 * Not actually a reason - but on your particular platform, look at the {{{java -X}}} options.
They may be VERY helpful.
 * Your classloaders are not being garbage collected.

'''How much memory is Tomcat/webapp/??? using?'''

 * To find out how much memory Tomcat is using, you might be able to use the Runtime class
provided by the JDK.
 * You can't find out how much memory a webapp is using. The JVM doesn't give us these detail.
 * You can't find out how much memory a ??? is using. The JVM doesn't give us these detail.
 * That being said, a memory profiling tool might prove the above statements wrong - but you
probably don't want to use them in a production environment.

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