Hello,
I am facing the problem that when the application has been running for a bit the connection pool gets exhausted sometimes. I was wondering the following

1) I currently have most of my queries (just selects) surrounded by a transaction, is this needed, I started my first example this way and continued with it. I know this is a must for update/insert/deletes but is it needed at all for selects.

2) When due to some exception transaction is not committed/rolled back but the associated session is closed, does the connection associated with the session get returned to the pool or not?

3) The

WARNING: afterTransactionCompletion() was never called

warning that is seen, is that cause for concern or can it be ignored?

4) If any of the above are not causes for connections being lost, what kind of code is normally responsible for the connection pool exhaustion problem.

FYI, all my session.open calls have an associated finally which does
if(sess != null)
sess.close();

Thanks,
Sohil

To answer your questions,

1) Always use transactions even for reads.

2) Sounds like a leak to me. You need to do your best to control resources such as database connections. Follow a good example where a finally block will complete the transacation and close the connection (eg return it to the pool). Maybe your best option is to consider using a TX framework. Spring is a good option.

3) This shows you are NOT closing your connection correctly thus have a resource leak. It should not be ignored.

4) See the examples in the documentation and some of the example code we supply. Alternatively, try out Spring's transaction wrappers.

--David

Using a pool like Proxool will help you to discover if you close/dispose your connections properly.

Proxool has a background HouseKeeper threads that does - amongst others - the following:
1/ make sure connections waiting in the pool are still 'working' and discard them if not;
2/ make sure active connections are not active since too long (maximum usage time).

If you do not release your connections properly, feature 2 will close those connections once the maximum lifetime is reached and log a warning message.

This way, you shouldn't reach out of connections, and you will be warned in case of miss-behavior.