How configure JVM to wait instead throwing OutOfMemoryError

Question

How to wait for garbage collector instead throwing OutOfMemoryError by JVM? Is there is some setting for JVM or othrer options (like code practices)?

I don't want to incement JVM memory settings or tuning GC - only wait for GC with no OutOfMemoryError cause I know there is no memory leaks, just garbage preventing new allocation.

Answer 1

I'm afraid, your question doesn't make a lot of sense.

An OutOfMemoryException is normally thrown after the GC has run and has been unsuccessful in reclaiming enough memory for you to proceed. Waiting for the GC to run (again) is unlikely to help. And if it doesn't help, the result is that your application will just freeze.

Besides, there isn't a way to do it.

Answer 2

You can probably tune the threshold for when the JVM will give up and throw OOM, but this is what the JVM does by design when it detects that garbage collection is not accomplishing anything. Note that the JVM will not throw an OOM because of bad timing or just because you've created a lot of objects. It will detect that it has repeatedly run GC and GC hasn't freed up any significant amount of memory.

Some possibilities:

1. You are using a lot of memory on a permanent basis. This isn't necessarily a memory leak, maybe you just load some huge data and don't realize how big it is in memory.
2. You have a memory leak or maybe you prefer "memory used in unexpected ways". Java offers lots of easy places to lose memory. I've been killed by ThreadLocal caches in a JSON library and failure to call new String(string) when appropriate.
3. Temporary data is drifting into PermGen because it doesn't act all that temporary.
4. You don't have any big problems, but you're pushing the envelope for the amount of memory you have allocated and you haven't tuned properly. Turn on concurrent mark sweep garbage collector, turn on GC logging, and see if behavior matches with your expectations of what the app is doing.

Lastly, run a profiler to see what you're using memory on. The first iteration of any program almost always has huge low hanging fruit to clean up.