src/UserGuide/latest-Table/API/Programming-MQTT.md

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# MQTT Protocol

## 1. Overview

MQTT (Message Queuing Telemetry Transport) is a lightweight messaging protocol designed for IoT and low-bandwidth environments. It operates on a Publish/Subscribe (Pub/Sub) model, enabling efficient and reliable bidirectional communication between devices. Its core objectives are low power consumption, minimal bandwidth usage, and high real-time performance, making it ideal for unstable networks or resource-constrained scenarios (e.g., sensors, mobile devices).

IoTDB provides deep integration with the MQTT protocol, fully compliant with MQTT v3.1 (OASIS International Standard). The IoTDB server includes a built-in high-performance MQTT Broker module, eliminating the need for third-party middleware. Devices can directly write time-series data into the IoTDB storage engine via MQTT messages.

![](/img/mqtt-table-en-1.png)


## 2. Configuration

By default, the IoTDB MQTT service loads configurations from `${IOTDB_HOME}/${IOTDB_CONF}/iotdb-system.properties`.

| **Property**            | **Description**                                                                                                | **Default** |
| ------------------------ | ---------------------------------------------------------------------------------------------------------------------- | ------------------- |
| `enable_mqtt_service`     | Enable/ disable the MQTT service.                                                                                    | FALSE             |
| `mqtt_host`               | Host address bound to the MQTT service.                                                                              | 127.0.0.1         |
| `mqtt_port`               | Port bound to the MQTT service.                                                                                      | 1883              |
| `mqtt_handler_pool_size`  | Thread pool size for processing MQTT messages.                                                                       | 1                 |
| **`mqtt_payload_formatter`** | **Formatting method for MQTT message payloads. ​**​**Options: `json` (tree model), `line` (table model).** | **json**    |
| `mqtt_max_message_size`   | Maximum allowed MQTT message size (bytes).                                                                           | 1048576           |

## 3. Write Protocol

* Line Protocol Syntax

```JavaScript
<measurement>[,<tag_key>=<tag_value>[,<tag_key>=<tag_value>]][ <attribute_key>=<attribute_value>[,<attribute_key>=<attribute_value>]] <field_key>=<field_value>[,<field_key>=<field_value>] [<timestamp>]
```

* Example

```JavaScript
myMeasurement,tag1=value1,tag2=value2 attr1=value1,attr2=value2 fieldKey="fieldValue" 1556813561098000000
```

![](/img/mqtt-table-en-2.png)

## 4. Naming Conventions

* Database Name

The first segment of the MQTT topic (split by `/`) is used as the database name.

```Properties
topic: stock/Legacy
databaseName: stock


topic: stock/Legacy/#
databaseName:stock
```

* Table Name

The table name is derived from the `<measurement>` in the line protocol.

* Type Identifiers

| Filed Value                                                        | IoTDB Data Type |
|--------------------------------------------------------------------| ----------------- |
| 1<br>1.12                                                          | DOUBLE          |
| 1`f`<br>1.12`f`                                                    | FLOAT           |
| 1`i`<br>123`i`                                                     | INT64           |
| 1`u`<br>123`u`                                                     | INT64          |
| 1`i32`<br>123`i32`                                                 | INT32           |
| `"xxx"`                                                            | TEXT            |
| `t`,`T`,`true`,`True`,`TRUE`<br> `f`,`F`,`false`,`False`,`FALSE`   | BOOLEAN         |