how to make a jvm do garbage collection externally

Question

I have an application deployed to production which sometimes throws OutOfMemory exception due to some memory leak. It is running on a headless ubuntu box on which I would prefer not to connect visualvm, jconsole etc remotely. Is there a way to make the jvm do gc (like in visualvm where you just click a button to do it).

I would like to run jmap -histo:live <pid> and this gc commands alternatively to find out which objects are surviving a gc. Which object numbers are growing etc. Right now I can see some unexpected object counts but it is happening across a number of my domain objects so I am not sure if it is a delayed gc or a memory leak.

So in short, I am looking for the linux command to be run against a jvm pid to cause it to do gc. Not system.gc.

Answer 1

The GC will aggressively try to clean up unreferenced objects as the heap gets full. So its not a "delayed gc". I think you are on the right track, use jmap and get a heap dump. Then analyze it to see what application objects are surviving that should not be. You may need to get a couple heap dumps and compare them against each other.

Answer 2

It's pretty hard to get a real memory leak in Java. If you're getting an out of memory error, then it most likely means that you're actually running out of memory. So to fix this, you need to find references to unused objects and clean them up manually. Because otherwise, the garbage collector can't free up the wasted memory.

When the JVM can't allocate any more memory, the garbage collector should automatically run.