@Override
  public UUID getOriginatingClusterId() {
    return clusterIds.isEmpty() ? HConstants.DEFAULT_CLUSTER_ID : clusterIds.get(0);
  }
@return the cluster id on which the change has originated. It there is no such cluster, it
        returns DEFAULT_CLUSTER_ID (cases where replication is not enabled)
hbase-server/src/main/java/org/apache/hadoop/hbase/wal/WALKeyImpl.java