Hi guys, what's the best framework for this problem?

I have a servlet which has to perform a "main" insert and a set of "subinserts".
in pseudo language:



Now, since a child category insert may fail and I will still be happy with the global transaction, I need to insert the subcategories in a separate session/transaction, like this



so that I can still use the mainsession for later use.

This would work except that i run in leaking connections. (if I have two free connections in my pool, two thread may get simoultaneously to "subsession.open") and I get in dead lock.
Once I solved the problem using two different connection pools for the session and the subsession but I wonder if there is a better solution.

Any ideas?
Thanx,
Roberto

I may miss understand you issue but is usualy best to avoid nested transactions. You can serialise your Tx operations, eg, pCode

session.open
insert a category;
session.close
session.open
for(1 to 10) {
insert a child category.
}
session.close


You could move the second session/Tx inside the loop if you wish to not have all child insert operations under the one transaction.

You are right.
Unfortunately serialization is sometimes impossible, like in the "open session in view", where a session is opened and closed before and after "everithing".
/rob

A deadlock can be avoided with a single connection pool too, via proper configuration: For example, Resin's pool (http://www.caucho.com/resin-3.0/db/config.xtp) supports a "max-overflow-connections" parameter, specifying how many "overflow connections" may be created when a connection wait times out.

So if two main Sessions should block because each is waiting for a sub-connection from a pool that doesn't have any idle connecitons left, they would receive an "overflow connection" after the specified wait time. If no overflow is configured, an exception would get thrown after the wait time - so no deadlock in any case (as far as I see).

The general demarcation problem can be solved by transaction infrastructure through a "transaction suspension" option. EJB CMT offers the transaction attribute "REQUIRES_NEW", which will suspend the current transaction, execute within a new one, then resume the old transaction. If Hibernate Sessions are bound to those transactions, this seems to be exactly what you're trying to achieve.

Of course, with EJB, you'd need to write corresponding Hibernate Session management yourself, because EJB will just care about its JTA transactions.

The upcoming Spring Framework release 1.0 RC1 offers such transaction suspension for POJOs, as a new feature of its generic transaction infrastructure. Resources like Hibernate Sessions are automatically bound to transactions, therefore will get suspended and resumed with transactions. This works with all of Spring's transaction strategies, for example HibernateTransactionManager and JtaTransactionManager.

As a side note, you can use multiple DataSources and multiple SessionFactories in Spring, either each with their own transaction management or with JTA transactions spanning all of them.

Juergen
Spring Framework developer
http://www.springframework.org
http://www.hibernate.org/110.html