FAQ / Memory
Table of Contents |
---|
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:
Wiki Markup \[http://marc.theaimsgroup.com/?t=104388973000006&r=1&w=2 java.lang.OutOfMemoryError during deploy\]
Wiki Markup \[http://marc.theaimsgroup.com/?t=104378347700007&r=1&w=2 Memory requirements\]
Wiki Markup \[http://marc.theaimsgroup.com/?t=104333066400004&r=1&w=2 Memory Mgmt Tomcat\]
Wiki Markup \[http://marc.theaimsgroup.com/?t=103011379700006&r=1&w=2 Tomcat Out of memory\]
Wiki Markup \[http://marc.theaimsgroup.com/?t=104519961700002&r=1&w=2 Tracking memory usage over time\] \\
Wiki Markup |
---|
Also look at |
Questions
\[http://java.quest.com/jprobe/jprobe.shtml JProbe\], \[http://www.yourkit.com/ YourKit\] 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
Wiki Markup \[#Q1 How do I adjust memory settings?\]
Wiki Markup \[#Q2 Why do I get {{OutOfMemoryError}} errors?\]
Wiki Markup \[#Q3 How much memory is
- How do I adjust memory settings?
- Why do I get OutOfMemoryError errors?
- How much memory is
Tomcat/webapp/??? using?\] \\
Answers
Anchor
First look at java -X
to determine what parameters to set. Then you can set them via the environment variable CATALINA_OPTS
(using JAVA_OPTS
also works, but is not recommended). This variable is usually set in a file bin/setenv.sh
or bin/setenv.bat
that you may need to create by yourselves.The setenv
file is documented in RUNNING.txt in your version of Tomcat. The environment variables are described in a comment at the top of . Read the files catalina.bat or catalina.sh files. Anchor
Why do I get OutOfMemoryError
errors?
...
- 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. Theulimit
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. Quadrupling 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.
.Wiki Markup \[http://opensource2.atlassian.com/confluence/spring/pages/viewpage.action?pageId=2669 Your classloaders are not being garbage collected
- You run out of process memory (non java/GC memory), for example when using java.util.zip classes or JNI classes allocating process memory. See Instantiating Inflater/Deflater causes OutOfMemoryError; finalizers not called promptly enough
See also OutOfMemory and MemoryLeakProtection.
\]. \\
Anchor
- 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.
...