[MathMonkeyMan]

I have no idea, but the in-house pub/sub tech at a previous job used [PGM][1] together with some hand-written brokers and a client library. The overall delivery guarantee is at-most-once, but in over ten years and across tens of thousands of machines in multiple datacenters, they never saw a single dropped message. Not sure how they measured that, but I was told the measurements were accurate.

Well, except for that one major outage where everything shit the bed due to some misconfiguration of IP multicast in the datacenters, or so I was told.

So, maybe if your mission isn't life critical, you can just wrongfully assume exactly-once delivery.

[1]: https://en.wikipedia.org/wiki/Pragmatic_General_Multicast