public void commit() {
   preCommit();
   if (isSystemTransaction()) {
     _client.write(Msg.COMMIT_SYSTEMTRANS);
   } else {
     _client.write(Msg.COMMIT.getWriter(this));
     _client.expectedResponse(Msg.OK);
   }
 }
 @Override
 public long versionForId(int id) {
   MsgD msg = Msg.VERSION_FOR_ID.getWriterForInt(systemTransaction(), id);
   _client.write(msg);
   return _client.expectedBufferResponse(Msg.VERSION_FOR_ID).readLong();
 }