Jboss java.lang.OutOfMemoryError：Java堆空间

Question

from time to time jboss serwer throws "An unhandled exception has occurred:

java.lang.OutOfMemoryError: Java heap space".

Could you please explain me how it works?

A few infromation: Jboss is running all the time in standalone mode on Windows. From standalone.conf "JAVA_OPTS=-Xms1G -Xmx1G -XX:MaxPermSize=256M" I deploy ~50MB war file, after tests I remove it.

What is possible cause of this Java heap space exception? Should I restart server between following deploys? Is there any command to clean heap space? If I understand corectly increasing of -Xmx argument will not help. It will only delay the appearance of the exception. Right?

Thanks in advance

Answer 1

What is possible cause of this Java heap space exception?

On the face of it, the explanation is simple. The JVM has run out of heap space, and the GC is unable to reclaim enough space to continue.

But what caused the JVM to get into that state?

There are a number of possible explanations, but they mostly fall into three classes:

1. Your application has a memory leak.

2. Repeated deploys are causing memory to leak.

3. There are no memory leaks, but occasionally your application is getting a request that simply needs too much memory.

Should I restart server between following deploys?

That may help if the deploys are causing the leaks. If not, it won't.

Is there any command to clean heap space?

There is no command that will do this. The JVM will already have run a "full" GC before throwing the OOME.

If I understand corectly increasing of -Xmx argument will not help. It will only delay the appearance of the exception. Right?

That depends. If the root cause is #3 above, then increasing the heap size may solve the problem. But if the root cause is #1 or #2, then tweaking the heap size will (at best) cause the JVM to survive longer between crashes.

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My recommendation is to start by treating this as a "normal" (cause #1) memory leak, and use a memory profiler to identify and fix leaks that are likely to build over time.

If / when you can definitively eliminate cause #1, consider the others.

Answer 2

Please increase the MaxPermSize variable and check it will work.

JAVA_OPTS=-Xms1G -Xmx1G -XX:MaxPermSize=512M

Answer 3

I absolutely agree with the answer from Stephen C , i just want to show you a possible way how you can analyse it.

A minimal tool for monitoring the memory is jstat and comes with JDK . After starting JBoss you can start monitoring the memory and GC with

jstat -gc <JBOSS_PID> 2s

The output can then be loaded for example in an excel.

Now when you recognize something strange happens with the memory, take a heap dump:

jcmd <JBOSS_PID> GC.heap_dump <filename>

jcmd also comes with JDK .

You can than load the heap dump into MAT and analyse it. It takes some practice and patience to work with MAT. They also have a good Tutorial . You can also compare heap dumps in MAT.

I also suggest you add XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=<path>" to your JAVA_OPTS.