Backends

MQTT Message Persistence

One-to-one message Persistence

1. PUB publishes a message;
2. Backend records this message in DB;
3. SUB subscribes to a topic;
4. Backend retrieves the messages of this topic from DB;
5. Messages are sent to SUB;
6. Once the SUB acknowledged / received the message, backend removes the message from DB.

Many-to-many message Persistence

1. PUB publishes a message;
2. Backend records the message in DB;
3. SUB1 and SUB2 subscribe to a topic;
4. Backend retrieves the messages of this topic;
5. Messages are sent to SUB1 and SUB2;
6. Backend records the read position of SUB1 and SUB2, the next message’s retrieval starts from this position.

Client Connection State

EMQX supports retaining the client's connection state in Redis or DB.

Client Subscription by Broker

EMQX Persistence supports subscription by broker. When a client goes online, the persistence module loads the subscriptions of the client from Redis or Databases.

List of Persistence Plugins

EMQX allowes storing messages in Redis, MySQL, PostgreSQL, MongoDB, Cassandra, DynamoDB, InfluxDB, OpenTSDB and Timescale:

Persistence Plugins	Config File	Description
emqx_backend_redis	emqx_backend_redis.conf	Redis Message Persistence
emqx_backend_mysql	emqx_backend_mysql.conf	MySQL Message Persistence
emqx_backend_pgsql	emqx_backend_pgsql.conf	PostgreSQL Message Persistence
emqx_backend_mongo	emqx_backend_mongo.conf	MongoDB Message Persistence
emqx_backend_cassa	emqx_backend_cassa.conf	Cassandra Message Persistence
emqx_backend_dynamo	emqx_backend_dynamo.conf	DynamoDB Message Persistence
emqx_backend_influxdb	emqx_backend_influxdb.conf	InfluxDB Message Persistence
emqx_backend_opentsdb	emqx_backend_opentsdb.conf	OpenTSDB Message Persistence
emqx_backend_timescale	emqx_backend_timescale.conf	Timescale Message Persistence