2phase-commit

I am trying to understand how three-phase commit avoids blocking Consider the following two failure scenarios: Scenario 1: In phase 2 the coordinator sends preCommit messages to all cohorts and has gotten an ack from all except cohort A. Network problems prevent cohort A from receiving the coordinator's preCommit message. Cohort A times out waiting for the preCommit message and chooses to abort. Then both the coordinator and cohort A crash. Scenario 2: The protocol reaches phase 3. The coordinator sends a doCommit message to cohort A. But before it can send more doCommit messages the

I have a very simple scenario involving a database and a JMS in an application server (Glassfish). The scenario is dead simple: 1. an EJB inserts a row in the database and sends a message. 2. when the message is delivered with an MDB, the row is read and updated. The problem is that sometimes the message is delivered before the insert has been committed in the database. This is actually understandable if we consider the 2 phase commit protocol: 1. prepare JMS 2. prepare database 3. commit JMS 4. ( tiny little gap where message can be delivered before insert has been committed) 5. commit