We achieved this at Hotmail 2 decades ago by trading latency for correctness. Publisher: do at least once delivery, but only up to the next k minutes. Each su

We achieved this at Hotmail 2 decades ago by trading latency for correctness. Publisher: do at least once delivery, but only up to the next k minutes. Each subscriber has a bitset of received IDs, filtering out redeliveries. Every 2*k minutes, bitset can be GC’d.