The Message Queuing Telemetry Transport (MQTT) protocol is ideal for connecting remote devices with a small code footprint and minimal network bandwidth. MQTT today is used in a wide variety of industries, such as automotive, manufacturing, telecommunications, oil and gas, etc.

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Prerequisites

Before sinking data from RisingWave to an MQTT topic, please ensure the following:
  • The RisingWave cluster is running.
  • An MQTT broker is running and accessible from your RisingWave cluster.
  • Create an MQTT topic that you want to sink data to.
  • You have permission to publish data to the MQTT topic.
For example, we have an iot_sensor_data table in RisingWave that stores data from various IoT devices at a given timestamp, including temperature and humidity readings, along with a status field indicating whether the device is in a normal or abnormal state. For more information to learn about MQTT and get started with it, refer to the MQTT guide.

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Syntax

To sink data from RisingWave to an MQTT topic, create a sink using the syntax below: 
CREATE SINK [ IF NOT EXISTS ] sink_name
[FROM sink_from | AS select_query]
WITH (
   connector='mqtt',
   url = '<your MQTT server>:<port>',
   topic = '<topic>',
   qos =  '<qos_level>',
   type = '<append-only>'
   username = '<your user name>',
   password = '<your password>')
FORMAT PLAIN ENCODE data_encode -- Format options: plain (encode BYTES and JSON) (
    force_append_only='true',
);
This query sets up an MQTT sink mqtt_sink to forward data from iot_sensor_data to an MQTT server. It configures the MQTT connector, server URL, target topic, data type, message retention, quality of service, and JSON encoding. 
CREATE SINK mqtt_sink
FROM iot_sensor_data
WITH
(
    connector='mqtt',
    url='tcp://mqtt-server',
    topic= 'sink_iot_data',
    type = 'append-only',
    retain = 'true',
    qos = 'at_least_once',
) FORMAT PLAIN ENCODE JSON (
    force_append_only='true',
);
After the sink is created, you will continuously consume the data in the MQTT topic from RisingWave in append-only mode.

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Parameters

FieldNotes
urlRequired. The URL of the broker to connect to, e.g., tcp://localhost. Must be prefixed with tcp://, mqtt://, ssl://, or mqtts:// to denote the protocol. mqtts:// and ssl:// use native certificates if no CA is specified.
qosOptional. The quality of service for publishing messages. Defaults to at_most_once. Options include at_most_once, at_least_once, or exactly_once.
usernameOptional. Username for the MQTT broker.
passwordOptional. Password for the MQTT broker.
client_prefixOptional. Prefix for the MQTT client ID. Defaults to “risingwave”.
clean_startOptional. Determines if all states from queues are removed when the client disconnects.
  • If true, the broker clears all client states upon disconnect;
  • If false, the broker retains the client state and resumes pending operations upon reconnection.
inflight_messagesOptional. Maximum number of inflight messages. Defaults to 100.
tls.client_certOptional. Path to the client’s certificate file (PEM) or a string with the certificate content. Required for client authentication. Can use fs:// prefix for file paths.
tls.client_keyOptional. Path to the client’s private key file (PEM) or a string with the private key content. Required for client authentication. Can use fs:// prefix for file paths.
topicOptional. The topic name to subscribe or publish to. Can include wildcard topics, e.g., /topic/#.
topic.fieldOptional. Enables dynamic writing to multiple topics based on the value of a specified column. If set, the target topic is the value of this column.
retainOptional. Whether the message should be retained by the broker.
r#typeRequired. Type identifier.