@Override
  public List<ServerName> listAllReplicators() throws ReplicationException {
    Set<ServerName> replicators = new HashSet<>();
    Scan scan = new Scan().addFamily(QUEUE_FAMILY).setFilter(new KeyOnlyFilter())
      .setReadType(ReadType.STREAM);
    try (Table table = conn.getTable(tableName); ResultScanner scanner = table.getScanner(scan)) {
      for (;;) {
        Result result = scanner.next();
        if (result == null) {
          break;
        }
        ReplicationQueueId queueId = ReplicationQueueId.parse(Bytes.toString(result.getRow()));
        replicators.add(queueId.getServerName());
      }
    } catch (IOException e) {
      throw new ReplicationException("failed to listAllReplicators", e);
    }
    return new ArrayList<>(replicators);
  }
HBase table based replication queue storage.
hbase-replication/src/main/java/org/apache/hadoop/hbase/replication/TableReplicationQueueStorage.java