What happens if there is an error during a commit?

Question

What happens if an error occurs while committing a transactional resource?
          For example, say the transaction manager successfully sends a commit
          notification to two transactional resources at the end of a transaction, but
          then gets an error while trying to commit a third one. It can't rollback the
          first two because they've already been committed. Is it up to the client to
          perform forensics in this case, or is it too rare to account for?
          Bob
          

Answer 1

Bob,
          This is exactly the problem that is solved by "2 phase commit" of transactions.
          The JTA transaction manager will not tell the 3 resources to commit. Instead,
          it will tell them all to "prepare" - it is the resources' responsibility to
          confirm that they have prepared only when they have written the post transaction
          stast to disk and KNOW that they can commit, if required, in the future.
          When all 3 prepares have returned OK, the transaction manager writes a record to
          disk confirming its decision to commit. Only then will it go ahead and tell the
          resources to commit.
          Hence, in your secnario, the 3rd prepare will fail and the transaction manager
          will tell the other 2 resources to roll back.
          Of course, if something catastrophic happened (disk head crash, fire...) then a
          commit may fail, leaving the results inconsistent as in your scenario. This is
          termed a "Heuristic completion" and you need to send in the DBAs to take care of
          the forenzics that you are worried about.
          For a more detailled discussion of this, take a look at
          http://dev2dev.bea.com/articlesnews/discussion/thread.jsp?forum=1&thread=106
          I hope that helps,
          Peter.
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          Bob Lee wrote:
          > What happens if an error occurs while committing a transactional resource?
          >
          > For example, say the transaction manager successfully sends a commit
          > notification to two transactional resources at the end of a transaction, but
          > then gets an error while trying to commit a third one. It can't rollback the
          > first two because they've already been committed. Is it up to the client to
          > perform forensics in this case, or is it too rare to account for?
          >
          > Bob
          >
          >
          >