How to handle OutOfMemoryError in Java? [duplicate]

Answer 1

Start java with a larger value for option -Xmx, for instance -Xmx512m

Answer 2

Before taking any dangerous, time-consuming or strategic actions, you should establish exactly what in your program is using up so much of the memory. You may think you know the answer, but until you have evidence in front of you, you don't. There's the possibility that memory is being used by something you weren't expecting.

Use a profiler. It doesn't matter which one, there are plenty of them. First find out how much memory is being used up by each object. Second, step though iterations of your serializer, compare memory snapshots and see what objects or data are created.

The answer will most likely be to stream the output rather than building it in memory. But get evidence first.

Answer 3

You get an OutOfMemoryError because your program requires more memory than the JVM has available. There is nothing you can specifically do at runtime to help this.

As noted by krosenvold, your application may be making sensible demands for memory but it just so happens that the JVM is not being started with enough (e.g. your app will have a 280MB peak memory footprint but the JVM only starts with 256MB). In this case, increasing the size allocated will solve this.

If you feel that you are supplying adequate memory at start up, then it is possible that your application is either using too much memory transiently, or has a memory leak. In the situation you have posted, it sounds like you are holding references to all of the million items in memory at once, even though potentially you are dealing with them sequentially.

Check what your references are like for items that are "done" - you should deference these as soon as possible so that they can be garbage collected. If you're adding a million items to a collection and then iterating over that collection, for example, you'll need enough memory to store all of those object instances. See if you can instead take one object at a time, serialise it and then discard the reference.

If you're having trouble working this out, posting a pseudo-code snippet would help.

Answer 4

There's no real way of handling it nicely. Once it happens you are in the unknown territory. You can tell by the name - OutOfMemoryError. And it is described as:

Thrown when the Java Virtual Machine cannot allocate an object because it is out of memory, and no more memory could be made available by the garbage collector

Usually OutOfMemoryError indicates that there is something seriously wrong with the system/approach (and it's hard to point a particular operation that triggered it).

Quite often it has to do with ordinary running out of heapspace. Using the -verbosegc and mentioned earlier -XX:+HeapDumpOnOutOfMemoryError should help.

You can find a nice and concise summary of the problem at javaperformancetuning

Answer 5

In addition to some of the tips that have been give to you, as review the memory lacks and also start the JVM with more memory (-Xmx512M). Looks like you have a OutOfMemoryError cause your TopicParser is reading a line that probably is pretty big (and here is what you should avoid), you can use the FileReader (or, if the encoding is an issue, an InputStreamReader wrapping a FileInputStream). Use its read(char[]) method with a reasonably sized char[] array as a buffer.

Also finally to investigate a little why is the OutOfMemoryError you can use -XX:+HeapDumpOnOutOfMemoryError Flag in the JVM to get a dump heap information to disk.

Good luck!

Answer 6

Everyone else has already covered how to give Java more memory, but because "handle" could conceivably mean catch, I'm going to quote what Sun has to say about Errors:

An Error is a subclass of Throwable that indicates serious problems that a reasonable application should not try to catch. Most such errors are abnormal conditions.

(emphasis mine)