joule-moq-relay: an object is held once, and the socket keeps what arrives #583

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dcharlot merged 2 commits from relay/fanout-load into main 2026-11-02 18:36:39 -05:00

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2026-11-02

Transaction Science

joule-moq-relay: an object is held once, and the socket keeps what arrives ...

Under load the relay collapsed with cores to spare, for two reasons a load
test showed.

Its one UDP socket kept the kernel's default buffer, about 212 KB. Each
fan-out's acknowledgements arrive together, so at 2,000 viewers of 2 Mbit/s the
kernel dropped about a million packets in 20 seconds. A dropped acknowledgement
reads as loss: a retransmission and a smaller congestion window. The buffer is
now a setting, 4 MiB by default, for the sockets the relay listens on and dials
from. The system caps it, so the relay warns when it gets less.

Each subscriber also got its own copy of every payload, while the fan-out held
the relay's one lock, and two more copies on the way to the wire. An object is
now held once, from when it is read until the last QUIC stream has it
acknowledged. The cache, every session's queue and every QUIC send buffer share
one allocation, and a keyframe stops being N keyframes in memory. A transport
that keeps no buffers still copies, once, where it writes, and a bridge to an
earlier draft still gets an object's head and payload as one write.

`examples/fanout_load.rs` is the load test. A bystander on its own track measures
what the audience costs everyone else on the relay.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

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2026-11-02 13:26:10 -05:00

Transaction Science

joule-moq-relay: a fan-out load test: one publisher, N subscribers, a bystander, the relay's own memory and CPU ...

Co-Authored-By: Claude Opus 5.5 <[email protected]>

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2026-11-02 12:46:37 -05:00