[mosquitto-dev] Throughput degrades as number of subscriptions grows

[V Z <uvzubovs@xxxxxxxxx>]

Hello. I ran a test using Java Paho client with 1 producer and N consumers. Each consumer had unique number and subscribed to /c followed by that number, i.e. /c1, /c2, etc. Producer published 1000 byte message round robbin to these topics with qos=0. Under this setup any one message was delivered to only one consumer.

I collected the following throughput numbers:

50,000 messages per second when N=1
25,000 messages per second when N=100
15,000 messages per second when N=200
  7,000 messages per second when N=500
  3,500 messages per second when N=1000

The messages per second above is the total throughput from the producer perspective, not per consumer.

I wonder why it gets lower and lower. Is it because the broker has more subscriptions to check to see where else to send the message? If so, is topic to subscription matching that inefficient?

Thanks!