code: public void rollback(Xid xid) throws XAException
     {
        if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled()) SibTr.entry(this, tc, "rollback", xid);
  
        internalRollback(xid);
        
        if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled()) SibTr.exit(this, tc, "rollback");
     }
docs: Called by the transaction manager to inform us to rollback the work
  done as part of this transaction.
  <p>
  Across the wire we will flow:
  <p>
  BIT32    TransactionId
  The XID Structure
  
  @param xid
  
  @throws XAException if an exception is thrown at the ME. In the
  event of a comms failure, an XAException with XAER_RMFAIL will
  be thrown.