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From Michael Pflueger <>
Subject Memory Management, reading huge tables fills heap space
Date Thu, 04 Aug 2011 14:33:28 GMT

I'm reading a huge table with openJPA in chunks, like this:

List list = query.setMaxResults(batchSize).setFirstResult(position * batchSize).getResultList();

And iterate over it like this:

		for (Entity e : list) {

Now my Java Heap Space fills slowly up to around close to 100%, then stays around that value,
sometimes it starts fluctuating...

Now I uncommented entityManager.detach(e), but it behaves more or less the same, it fills
my whole heap space.
In small tests I have not gotten an OutOfMemoryException yet, but the bigger production app
I need this for already got some after some runtime...

I don't really understand this behavior, is there anything I can do about it?
I already tried removing the detached state field from the Entity but that does not seem to
help either.

What does help is repeatedly calling entityManager.clear() to clear the whole context, but
this solution might not always be desireable.

So, besides possible solutions I also wonder if this behavior is "normal" or whether I should
try to create a small testCase for this aswell.


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