mosquitto mqtt broker won’t send more than 20 publish packets to subscriber

I’m currently working on a MQTT client using python, and come to the point where i can create clients that publish and subscribe to the Mosquitto broker.

The problem is that, no matter what, the mosquitto broker will send only a maximum of 20 PUBLISH packets to a subscriber client, even if it stay connected for long periods of time.

How can I configure mosquitto to send more than 20 PUBLISH packets to the subscriber client?

Mosquitto log:

1608918436: Received PUBLISH from publisher (d1, q1, r0, m1, '/OS', ... (3 bytes))
1608918436: Sending PUBLISH to subscriber (d0, q1, r0, m17, '/OS', ... (3 bytes))
1608918436: Sending PUBACK to publisher (m1, rc0)
1608918438: Received PUBLISH from publisher (d1, q1, r0, m1, '/OS', ... (3 bytes))
1608918438: Sending PUBLISH to subscriber (d0, q1, r0, m18, '/OS', ... (3 bytes))
1608918438: Sending PUBACK to publisher (m1, rc0)
1608918440: Received PUBLISH from publisher (d1, q1, r0, m1, '/OS', ... (3 bytes))
1608918440: Sending PUBLISH to subscriber (d0, q1, r0, m19, '/OS', ... (3 bytes))
1608918440: Sending PUBACK to publisher (m1, rc0)
1608918442: Received PUBLISH from publisher (d1, q1, r0, m1, '/OS', ... (3 bytes))
1608918442: Sending PUBLISH to subscriber (d0, q1, r0, m20, '/OS', ... (3 bytes))

at this point, the mosquitto broker won’t send more packets to the subscriber, excepting PINGRESP when the subscriber client sends PINGREQ in order to remain connected to the broker.

1608918442: Sending PUBACK to publisher (m1, rc0)
1608918442: Received PINGREQ from subscriber
1608918442: Sending PINGRESP to subscriber
1608918444: Received PUBLISH from publisher (d1, q1, r0, m1, '/OS', ... (3 bytes))
1608918444: Sending PUBACK to publisher (m1, rc0)
1608918446: Received PUBLISH from publisher (d1, q1, r0, m1, '/OS', ... (3 bytes))
1608918446: Sending PUBACK to publisher (m1, rc0)

I’ll be happy to provide the code for the client if it’s actually needed.

Later edit: Maybe it’s worth mentioning
If there are more subscribers on one topic, this behavior is not observable, the broker sends packets without stopping at any point whatsoever.

Answer

20 messages sounds like you are hitting the max number of inflight messages (max number of unacknowledged messages)

The messages are QOS 1 so your client needs to acknowledge them.

Advertisement

Answer