Hi,

I've been using Hibernate for 2,5 months (currently using 2.1beta6) and when i was making carge tests to my application database, i got several memory problems. I run some memory profiles programs and I checked that The problem is related with Hibernate cache.

As long as I understood, Hibernate has 3 cache levels (correct me if i'm wrong):
- JCS cache, which is shared by all hibernate sessions;
- Session cache;
- Query cache.

JCS cache is optional, and is not causing any problems.

The problem is releated with session and query caches. When I load an object I do the following code:

private Object obj;
obj = (Object) session.load(Object.class, 1);

The loaded object will be duplicated in memory: in variable obj, and in Hibernate internal session cache. If insted of 1 object, I loaded a large number of objects with a large number of associations each one, I will run out of memory.

As a solution, I try to evict the object after loading it, but this as two problems:
- Evict doesn't work beacuse the memory never decreases;
- If it worked, it still would be a bad solution, because I was loading an object in cache to download it later. It's an waste of processor resources.

If I load an object by query, it's worst, beacuse that object and a few others will be loaded in query caches, and can not be evicted. Session.clear() doesn't work too, beacuse the memory never decreases.

In the worst case, if I load an object individualy, and next, load it within a collection, I will have the object replicated 3 times in memory: my java variable, hibernate session cache and hibernate query cache.

Other thing I don't understand is the diference between queries and criteria queries, in the cache context. Is there any diference between them? Or they both use cache in the same way?

I would like to NOT use any session and/or query cache. Is it possible? Hibernate cache it doesn't improve performance on my application, and it's giving me a lot of problems.

I read several posts about cache system and I saw that there are another users with the same problems, but the questions were spread by many posts and the answers were incomplete. I tryed to join everything in a same (long) post, and I would like to ask for hibernate team assistence.

Thanks in advance,
Joao Rangel

You should be closing and dereferencing the Session at the end of a transaction. Then the session cache will be garbage collected.

Your right, but i tried to do that, and session.close() did not release any memory either. I forgot to mention it in the previous post.

Then I don't think that your memory leak is in Hibernate :)

I suggest you inspect the source of session.close() to confirm that there is no possibility of a leak.

Are you restarting often and using C3P0 connection pooling with Hibernate? I posted a week or two back how I found that the version shipped with Hibernate has no way to close the connection pool so when you restart, it seems to get orphaned and hibernate appears to start up a new one ... thereby eating memory. I still have some memory problems in my Tomcat/Hibernate/Struts1.1 application but, for the life of me, I can't find them.

Regards,
David

I have the same problem, when I executed a query via a session,I got a list of my object, then I closed the session, I found something still referenced by the sessionFactory (the sessionFactory is a static variable of the type SessionFactory ),I want to know how to resovle the problem?