EddyDHH, the creator of the Ruby on Rails framework, decided to rewrite Campfire Once from Ruby on Rails to Rust.
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In a constant-rate test at 100 POSTs/s, increasing the Rust broadcast channel capacity from 256 to 16,384 raised event delivery from about 14% to 90%, but pMAX latency also increased from 11s to over 130s. Reconnecting clients fetch recent messages, so the delivery percentage alone does not tell us whether this improves their experience.
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In a constant-rate test at 100 POSTs/s, increasing the Rust broadcast channel capacity from 256 to 16,384 raised event delivery from about 14% to 90%, but pMAX latency also increased from 11s to over 130s. Reconnecting clients fetch recent messages, so the delivery percentage alone does not tell us whether this improves their experience.
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Before comparing speed, I need to check compatibility. A rewrite that changes database access or client behavior may be doing different work.
The Rust version uses a bounded channel for notifications. A client that falls behind can reconnect and fetch recent messages. A larger buffer lets more notifications wait, but that wait still matters.
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Later, in the benchmark discussion, I tested whether a larger buffer would help clients receive more notifications at the same request rate.
In a constant-rate test at 100 POSTs/s, increasing the Rust broadcast channel capacity from 256 to 16,384 raised event delivery from about 14% to 90%, but pMAX latency also increased from 11s to over 130s. Reconnecting clients fetch recent messages, so the delivery percentage alone does not tell us whether this improves their experience.
I would judge that trade-off by what people experience while using the chat, rather than by the delivery percentage alone.