[OASIS Issue Tracker] Commented: (MQTT-58) How many messages are received for overlapping subscriptions?

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    [ http://tools.oasis-open.org/issues/browse/MQTT-58?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=34667#action_34667 ] 

Richard Coppen commented on MQTT-58:
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There are benefits and drawbacks for Servers sending 1 or n messages to a Client with n subscribes with overlapping Topic Filters. 
Surely this should be a Server choice. Some Server implementations might optimize for performance and some may optimize for precision. In many cases sending a small number messages will likely out perform complex filtering of subscription patterns. This looks like a good case for a MAY clause.

In practice, subscribes with overlapping topic filters are likely to be rare as clients will know which topics they are subscribing to. 

How about the following as a proposal?

>>>

Where a Client has made multiple subscribes with overlapping Topic Filters, the Server MAY send one message per Client or one message per matching subscribe. 

<<<

> How many messages are received for overlapping subscriptions?
> -------------------------------------------------------------
>
>                 Key: MQTT-58
>                 URL: http://tools.oasis-open.org/issues/browse/MQTT-58
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Improvement
>          Components: core
>            Reporter: Allan Stockdill-Mander 
>
> A client has subscribed to a/+ with QoS2 and a/b with QoS1. A message is published to a/b. Does the client receive one or two messages? If one which QoS would apply?

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