External sync point coordination

A global unit of work can also be coordinated by an external X/Open XA-compliant transaction manager. Here the IBM MQ queue manager participates in, but does not coordinate, the unit of work.

The flow of control in a global unit of work coordinated by an external transaction manager is as follows:
  1. An application tells the external sync point coordinator (for example, TXSeries® ) that it wants to start a transaction.
  2. The sync point coordinator tells known resource managers, such as IBM MQ, about the current transaction.
  3. The application issues calls to resource managers associated with the current transaction. For example, the application could issue MQGET calls to IBM MQ.
  4. The application issues a commit or backout request to the external sync point coordinator.
  5. The sync point coordinator completes the transaction by issuing the appropriate calls to each resource manager, typically using two-phase commit protocols.

The supported levels of external sync point coordinators that can provide a two-phase commit process for transactions in which IBM MQ participates are defined at System Requirements for IBM MQ.

The rest of this section describes how to enable external units of work.