CODEWITHSUNDEEP
mqttbrokerhivemqmommqtt-vernemq
JetBrains
JetBrains

Reputation: 476

How does persistence session work in MQTT?

I use MQTT with QOS 1.

I have a consumer and a producer. They communicate with each other (HiveMQ as a client). They use VerneMQ as a broker. I use a persistence session.

If a consumer is offline and he goes later online, he should become all messages where he was offline. But that works only if consumer is on the other computer and I don't stop a micro service, but I turn off a WiFi and then turn it on. But if I shut down a micro service and then start it again that doesn't work with offline messages.

I think that's why it subscribes again on that topic, if I start a micro service again. Is it the reason? Or not?

UPDATE: I've just tested it without subscribing at the second start of the consumer. That doesn't work either. So subscribing is not the reason why the consumer doesn't get the messages.

Upvotes: 0

Views: 1348

Answers (1)

JetBrains
JetBrains

Reputation: 476

For persistence session, so that you become all messages when you were offline, you need some conditions to be satisfied:

1) turn off CleanStart on connect: 

Mqtt5Connect.builder()
            .cleanStart(false)
            .noSessionExpiry()
            .build()

2) collect remaining messages on connect with publishes

  mqttClient.publishes(MqttGlobalPublishFilter.REMAINING) {
        mqtt5Publish -> handleMessage(mqtt5Publish.topic.toString(), mqtt5Publish.payload.decodeContent())
    }

3) QOS 1+

That goes like a Swiss watch.

Upvotes: 1

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