MQTT nodes vs. in-flow processing

General
1

I'm doing a lot of MQTT message processing (central broker instance) and I'm wondering, what the more efficient approach would be:

  1. A lot of MQTT in / out nodes caring for very strict topics
  2. Doing all topic filtering / setting in the flow and working with only a minimum of MQTT nodes

Does it make a difference in established connections to the broker or the efficiency in processing?
Any insight is appreciated.

2

The MQTT nodes are already doing topic filtering to deliver the right message to the MQTT-in node since the connection to the broker is shared by all the nodes that have the same broker config node.

So having MQTT-in nodes per topic is probably more efficient than wildcards and then filtering again.

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3

As @hardillb already wrote: By subscribing to topics limiting data you really need the broker only transmit relevant data. This preserves bandwidth. Using many mqtt-innodes only adds subscriptions on the broker.
So a subscription to the root (#) or to data you only need a part of and have to discard later is not a good idea. The broker software like mosquito is written in C and in general faster than filtering inside node.js Node-Red.

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4

Thanks this clarifies this topic and confirms my "gut feelings". Appreciated.

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