[OJB-developers] concurrent broker transactions in single vm mode

[Doug C. <de...@fl...>]

A broker pool is required to implement odmg concurrent transactions
effectively. Daniel Fernandez, you have been looking at a broker pool
implementation; have you also thought about how to use this pool at
the odmg level in single vm mode?

Having looked at this a bit, it seems to me that one broker per odmg
transaction is a logical way to proceed. Most code that needs to
reference a broker is also grabbing a reference to a transaction.
Unfortunately a 1-1 relationship between DatabaseImpl and broker in
the current code is assumed by OJB.getBroker, but this can be fixed
pretty easily I think. Many places that get a broker from OJB either
can just as easily get it from the transaction, or don't care what
broker they end up with since they are just using it for access to the
cache or metadata.

For example, sequences such as (e.g., OQLQueryImpl.execute):

            // retrieve a broker instance
            PersistenceBroker broker = OJB.getInstance().getBroker();

            //obtain current ODMG transaction
            Transaction tx = OJB.getInstance().currentTransaction();

            // we allow queries even if no ODMG transaction is running.
            // thus we have to provide a pseudo tx if necessary
            boolean needsCommit = false;
            if (tx == null)
            {
                tx = OJB.getInstance().newTransaction();
            }

            // we allow to work with unopened transactions.
            // we assume that such a tx is to be closed after performing the query
            if (!tx.isOpen())
            {
                tx.begin();
                needsCommit = true;
            }

would get the trasaction first and become

            //obtain current ODMG transaction
            Transaction tx = OJB.getInstance().currentTransaction();

            // we allow queries even if no ODMG transaction is running.
            // thus we have to provide a pseudo tx if necessary
            boolean needsCommit = false;
            if (tx == null)
            {
                tx = OJB.getInstance().newTransaction();
            }

            // we allow to work with unopened transactions.
            // we assume that such a tx is to be closed after performing the query
            if (!tx.isOpen())
            {
                tx.begin();
                needsCommit = true;
            }
            // retrieve the transactions's broker instance
            PersistenceBroker broker = tx.getBroker();  // THE CHANGE


If you need a hand with this let me know. I am interested in seeing
the omdg layer improved with more concurrency for single vm
applications.

e