Prepared Transactions

Hello there,

I have a situation and would like to ask for your attention...

*Environment
*
JEE application running under JBossAS and using PostgreSQL 8.4.3 as backend.
In some transactions we use JMS queues and read/write database operations.
To have atomic transactions, we use 2PC/XA protocol that controls the
distributed commit/rollback across the resources.
The database connection is done through a xa-datasource set to use
org.postgresql.xa.PGXADataSource, which is the specific driver class for
distributed transactions.

*
Issue*

Sometimes i notice that some "Prepared Transactions" are dead in the
database without a commit/rollback operation, that is, from the
"pg_prepared_xacts" view i can see that the transaction is very old, it is
not a very long running transaction, i am sure. Checking another view,
"pg_locks", i can see the transaction in a "ShareLock" mode and, associated
with the same PID, another transaction in a "ExclusiveLock" mode. These
transactions use some database registers and keep these registers in this
lock state forever, preventing another new transaction to use these same
registers. As we have a Prepared Transactions blocked without a commit or
rollback, the new transactions stay waiting forever for the lock release. I
see, through a "ps" Linux command, many Postgres process with a "waiting"
status.

As we have a minimum occurrence of this issue, i was not able to identify
the real reason yet. Maybe it is bug related to my software, in Postgres, in
the driver version or even a specific Postgres configuration.

Nowadays, we have to perform a "ROLLBACK PREPARED" to clean the "dead"
Prepared Transaction, but it is not the right approach.

Do you have any tips or ideas about this situation?

Thanks in advance,
Marcelo