OpenHAB behavior on polling

I want to understand why the MQTT channels get flooded by messages reporting the state of items whereas they have not changed (ZWave binding, RFXCom binding, Amazon Echo binding).

I suppose this is due to periodical polling. After polling, only states of the device which have changed should be posted, isn’t it ?

Did you set-up the MQTT event bus?
From the docs:

Event Bus Binding Configuration
In addition to configuring MQTT publish/subscribe options for specific openHAB items, you can also define a generic configuration in the services/mqtt-eventbus.cfg file which will act on ALL status updates or commands on the openHAB event bus.

The mqtt event bus broadcasts ALL status UPDATES not just changes… And updates happen in the background all the time…

Yes the MQTT event bus is configured and this is where I miss some tricky setup to limit the MQTT traffic. I see 2 options:

  1. configure the MQTT topic name to seggregate messages per type of device and subscribe only to relevant topics on the listener side. But I don’t know if other placeholders than ${item} can be used in the topic name
  2. setup MQTT channel per item but this will be a huge work

I wouldn’t worry about the MQTT traffic, mosquitto is perfectly able to handle the load.
Most of the messages will end up broadcast by OH and not going anywhere after if you don’t subscribe to #

My concern is on the listener side (Eventghost) where all messages received are processed which tend to slow it down as the message list is scrolling fast because of this bunch of messages…

I am not familiar with eventGhost but can you not get it to subscribe only to the items you are interested in?