// enable group message
ZKHelixDataAccessor accessor = new ZKHelixDataAccessor(clusterName, new ZkBaseDataAccessor<ZNRecord>(_gZkClient));
Builder keyBuilder = accessor.keyBuilder();
IdealState idealState = accessor.getProperty(keyBuilder.idealStates("TestDB0"));
idealState.setGroupMessageMode(true);
accessor.setProperty(keyBuilder.idealStates("TestDB0"), idealState);
// registry a message listener so we know how many message generated
TestZkChildListener listener = new TestZkChildListener();
_gZkClient.subscribeChildChanges(keyBuilder.messages("localhost_12918").getPath(), listener);