private TConfigNodeHeartbeatReq genConfigNodeHeartbeatReq() {
    TConfigNodeHeartbeatReq req = new TConfigNodeHeartbeatReq();
    req.setTimestamp(System.nanoTime());
    return req;
  }
loop body of the heartbeat thread.
iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/manager/load/service/HeartbeatService.java