public long getTimestampOfLastShippedOp() {
    long lastTimestamp = 0L;
    for (long ts : lastShippedTimeStamps.values()) {
      if (ts > lastTimestamp) {
        lastTimestamp = ts;
      }
    }
    return lastTimestamp;
  }
Get the timestampsOfLastShippedOp, if there are multiple groups, return the latest one
hbase-server/src/main/java/org/apache/hadoop/hbase/replication/regionserver/MetricsSource.java