canique
commented
3 years ago I have done another test with a longer offline period (multiple hours). One exemplary topic [with no publishes during that offline time (or in the last weeks)] has been transmitted via the bridge 272 times. If I did another test, with 0 publishes on that topic, I'd see dozens of transmissions again. I know that QoS 1 only guarantees at least 1 transmission and does not make any guarantees about an upper boundary, but 272 times for a single topic does sound like a bug to me...
p.s.: Even changing both the bridge config as well as the publishing client to QoS 2 does not fix the problem. With QoS 2 - due to this bug - every publish on a topic is sent twice by the bridge after a reconnect. For topics that have rare publishes the same msg is sent over and over again. So if I publish msg A, the remote broker receives A, A. If I publish B to another topic less frequently, it seems that the remote broker receives the same B repeatedly with every publish to A's topic. This behaviour is a clear violation to the MQTT specification.
p.p.s: If MQTTv5 is used for the bridge connection, the mosquitto bridge sends duplicates infinitely. The other end closes the MQTT bridge connection with the error "Sent too many concurrent PUBLISH messages." - so mosquitto sends too fast in that case?
perfeldbak
svet-b
Here's the test procedure: 1) A few msgs are published locally to the mosquitto broker with retain flag set, on 1-2 topics. The broker has a bridge configured in OUT mode. The client publishing the msgs has set cleansession=false (weeks ago it was "true"). 2) When I pull the network cable from the linux machine running the broker, the bridge starts to enqueue msgs. This is perfectly fine. 3) After a couple of minutes, after plugging in the network cable again, the bridge sends out msgs from its queue. The problem is, it sends msgs from topics which have not been recently written at all. And it sends them DOZENs of times. I have counted 180 transmissions, although there are only 4 topics, and at maximum ~40 msgs could have been published in total while offline. The reconnect in the attached log file happens @ 1625652526. For example, the topic c32545676/sensors/air/92/wakeup_interval is not being actively used. As it has a retained msg, the msg should go out once on reconnect. But it is transmitted 45 times (!). The longer the offline time, the more often the msg is transmitted.
Tested on these mosquitto versions: 1.6.12, 2.0.11 Linux kernel: 4.19.59
excerpt from config file: