[jBoss-Dev] TransactionImpl

Carlos Pita Thu, 27 Jul 2000 17:39:22 -0700

Hi!

I have a question (it could be an observation if already had more self-confidence) about enlisting/delisting xa resources in the Transaction implementation. Here are the sources of both methods as they were in last week CVS repository (remember that resources is a Vector):

   public boolean delistResource(XAResource xaRes, int flag)
   {
        try {
            xaRes.end(xid, Status.STATUS_ACTIVE);
//            resources.removeElement(xaRes);
            return true;
        } catch(XAException e) {
            e.printStackTrace();
            return false;
        }
   }

   public boolean enlistResource(XAResource xaRes)
      throws RollbackException
   {
      // Check rollback only
      if (status == Status.STATUS_MARKED_ROLLBACK)
      {
         throw new RollbackException();
      }

      // Add resource
        try {
            xaRes.start(xid, Status.STATUS_ACTIVE);
            resources.addElement(xaRes);
            return true;
        } catch(XAException e) {
            e.printStackTrace();
            return false;
        }
   }

When the transaction commits (or rollback) the algorithm is:

[...]

for (int i = 0; i < resources.size(); i++)
{

               try
               {
                  ((XAResource)resources.elementAt(i)).commit(xid, false);
               } catch (XAException e)
               {
                  try {
                     ((XAResource)resources.elementAt(i)).forget(xid);
                  } catch(XAException another) {}
                  e.printStackTrace();
                  // TODO: what to do here?
               }
            }

So the question is:

What if we have more than one xa resource enlisted in the transaction corresponding to the same resource manager? I think that in this scenario the algorithm will run the 2 phase protocol against the same resource manager and for the same transaction more than once.

Regard this, the JTA spec says:

The enlistResource request results in the Transaction Manager informing the

resource manager to start associating the transaction with the work performed through

the corresponding resource—by invoking the XAResource.start method. The

Transaction Manager is responsible for passing the appropriate flag in its

XAResource.start method call to the resource manager. The XAResource interface

is described in section 3.4.

If the target transaction already has another XAResource object participating in the

transaction, the Transaction Manager invokes the XAResource.isSameRM method to

determine if the specified XAResource represents the same resource manager instance.

This information allows the TM to group the resource managers who are performing

work on behalf of the transaction.

1.Transaction Branch is defined in the X/Open XA spec [1] as follows: 'A global transaction has one or

more transaction branches. A branch is a part of the work in support of a global transaction for which the

TM and the RM engage in a separate but coordinated transaction commitment protocol. Each of the RM’s

internal units of work in support of a global transaction is part of exactly one branch. .. After the TM begins

the transaction commitment protocol, the RM receives no additional work to do on that transaction branch.

The RM may receive additional work on behalf of the same transaction, from different branches. The differ-ent

branches are related in that they must be completed atomically. Each transaction branch identifier (or

XID) that the TM gives the RM identifies both a global transaction and a specific branch. The RM may use

this information to optimise its use of shared resources and locks.'

That's all for now.

Thank you,

Carlos

[jBoss-Dev] TransactionImpl

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