[OASIS Issue Tracker] Commented: (MQTT-74) What should happen to messages pending delivery once the client sends unsubscribe?

[OASIS Issues Tracker <workgroup_mailer@lists.oasis-open.org>]

    [ http://tools.oasis-open.org/issues/browse/MQTT-74?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=34367#action_34367 ] 

Raphael Cohen commented on MQTT-74:
-----------------------------------

Hmmm...

In 2, the client received messages for a topic which it potentially thinks it has unsubscribed from. I can see that creating a lot of interesting head scratching when debugging a problem.

In 1, this stops a broker being able to immediately return a packet, and means it has to maintain a bit state, I suspect. It's also rather hard to define 'backlog', especially if one's internal design is a non blocking queue of some sort - no action can be taken based on an observation (a sort of Heisenberg-like thing, eg checking isEmpty then doing something. Think of the problem of incrementing a volatile int field in java).

3 would be my preference. It does not necessarily require a purge... It does fit nicely with the client's expectations.

However, we could leave the door open to 1 and 3. They're indistinguishable to the client.

> What should happen to messages pending delivery once the client sends unsubscribe?
> ----------------------------------------------------------------------------------
>
>                 Key: MQTT-74
>                 URL: http://tools.oasis-open.org/issues/browse/MQTT-74
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 3.1.1
>            Reporter: Richard Coppen
>             Fix For: 3.1.1
>
>
> A client might be too busy to process any more work, so sends UNSUBSCRIBE to turn the flow off. 
> Alternatively, the client may be unaware that a backlog of messages exists and sends UNSUBSCRIBE. 
> There are at lesat three possible options:
> 1. The server delays sending the UNSUBACK until the backlog is cleared
> 2. Send the UNSUBACK and then send the messages
> 3. Send the UNSUBACK and then purge the messages 
> The client's last defense should it not want the messages is to disconnect and reconnect with cleanSession set to (1)

-- 
This message is automatically generated by JIRA.
-
If you think it was sent incorrectly contact one of the administrators: http://tools.oasis-open.org/issues/secure/Administrators.jspa
-
For more information on JIRA, see: http://www.atlassian.com/software/jira