[Pharo-users] Re: Communication between different images

[Sven Van Caekenberghe]

> On 29 Jun 2021, at 20:10, Esteban Maringolo <emaring...@gmail.com> wrote:
> 
> I already got MQTT running, It's not completely clear to me how the
> QoS setting works (atLeastOnce, exactlyOnce, atMostOnce), I don't
> remember using that setting in Java (it probably had a sensible
> default).

From the comments in MQTTPacket class side

atMostOnce
        "Quality of service level 0 - no acks, send and forget"
        
        ^ 0

atLeastOnce
        "Quality of service level 1 - single acks, possible duplicates"
        
        ^ 1

exactlyOnce
        "Quality of service level 2 - no loss, no duplicates"
        
        ^ 2

The lowest one is the fastest, but won't work with persistent queues. In most 
cases the middle level is OK and enough - duplicates can only occur when you do 
not receive the ack.