Mixed outcomes and errors

Although the queue manager uses a two-phase commit protocol, this does not completely remove the possibility of some units of work completing with mixed outcomes. This is where some participants commit their updates and some back out their updates.

Units of work that complete with a mixed outcome have serious implications because shared resources that should have been updated as a single unit of work are no longer in a consistent state.

Mixed outcomes are mainly caused when heuristic decisions are made about units of work instead of allowing the queue manager to resolve in-doubt units of work itself. Such decisions are outside the queue manager's control.

Whenever the queue manager detects a mixed outcome, it produces FFST information and documents the failure in its error logs, with one of two messages:

• If a database manager rolls back instead of committing:

  AMQ7606 A transaction has been committed but one or more resource
          managers have rolled back.
  

• If a database manager commits instead of rolling back:

  AMQ7607 A transaction has been rolled back but one or more resource
          managers have committed.
  

Further messages identify the databases that are heuristically damaged. It is then your responsibility to locally restore consistency to the affected databases. This is a complicated procedure in which we need first to isolate the update that has been wrongly committed or rolled back, then to undo or redo the database change manually.

Parent topic: Considerations when contact is lost with the XA resource manager