MQTT Protocol

MQTT Protocol

MQTT is a machine-to-machine (M2M)/“Internet of Things” connectivity protocol. It was designed as an extremely lightweight publish/subscribe messaging transport. It is useful for connections with remote locations where a small code footprint is required and/or network bandwidth is at a premium.

IoTDB supports the MQTT v3.1(an OASIS Standard) protocol. IoTDB server includes a built-in MQTT service that allows remote devices send messages into IoTDB server directly.

Built-in MQTT Service

The Built-in MQTT Service provide the ability of direct connection to IoTDB through MQTT. It listen the publish messages from MQTT clients and then write the data into storage immediately. The MQTT topic is corresponding to IoTDB timeseries. The messages payload can be format to events by PayloadFormatter which loaded by java SPI, and the default implementation is JSONPayloadFormatter. The default json formatter support two json format, and the following is an MQTT message payload example:

 {
      "device":"root.sg.d1",
      "timestamp":1586076045524,
      "measurements":["s1","s2"],
      "values":[0.530635,0.530635]
 }

{
      "device":"root.sg.d1",
      "timestamps":[1586076045524,1586076065526],
      "measurements":["s1","s2"],
      "values":[[0.530635,0.530635], [0.530655,0.530695]]
  }

MQTT Configurations

The IoTDB MQTT service load configurations from ${IOTDB_HOME}/${IOTDB_CONF}/iotdb-engine.properties by default.

Configurations are as following:

NAME	DESCRIPTION	DEFAULT
enable_mqtt_service	whether to enable the mqtt service	false
mqtt_host	the mqtt service binding host	0.0.0.0
mqtt_port	the mqtt service binding port	1883
mqtt_handler_pool_size	the handler pool size for handing the mqtt messages	1
mqtt_payload_formatter	the mqtt message payload formatter	json
mqtt_max_message_size	the max mqtt message size in byte	1048576

Examples

The following is an example which a mqtt client send messages to IoTDB server.

        MQTT mqtt = new MQTT();
        mqtt.setHost("127.0.0.1", 1883);
        mqtt.setUserName("root");
        mqtt.setPassword("root");
        BlockingConnection connection = mqtt.blockingConnection();
        connection.connect();
        Random random = new Random();
        for (int i = 0; i < 10; i++) {
            String payload = String.format("{\n" +
                    "\"device\":\"root.sg.d1\",\n" +
                    "\"timestamp\":%d,\n" +
                    "\"measurements\":[\"s1\"],\n" +
                    "\"values\":[%f]\n" +
                    "}", System.currentTimeMillis(), random.nextDouble());
            connection.publish("root.sg.d1.s1", payload.getBytes(), QoS.AT_LEAST_ONCE, false);
        }
        connection.disconnect();
    }