code: @Override
      public int prepare(final Xid _xid)
      {
          if (JDBCStoreResource.LOG.isDebugEnabled()) {
              JDBCStoreResource.LOG.debug("prepare (xid = " + _xid + ")");
          }
          return 0;
      }
docs: Ask the resource manager to prepare for a transaction commit of the
  transaction specified in xid. (used for 2-phase commits).
  @param _xid  global transaction identifier (not used, because each file
  with the file id gets a new VFS store resource instance)
  @return always 0