Measured with `make bench-engine` against a real Redis: 103.6 -> 164.4
messages a second on a five-node chain (p50 latency 2125 -> 1171 ms) and
34.8 -> 63.2 on a fan-out of twenty. Against the memory backend, which is
what a pip install runs on, 262 -> 626.
The two that bought most of it:
- `StateBackend.record` puts a published value, its timestamp, its series
and its version counter in one round trip. They were four calls building
four pipelines, and a value crossing an edge pays them twice. A released
rate-limit hold rides along instead of a DEL per port.
- the readiness check reads a node's inputs and hands them to the node,
rather than reading the triggering ones to count them and having the node
read the same keys again a moment later.
`apply_outputs` was a second copy of `_record_outputs` and is now the same
code plus the event that distinguishes it.
The rest, each small:
- `_derive` builds a node-by-id map and a `consumes` index, so dispatching
an item and publishing a value stop scanning every node in the
installation.
- `read_all` is memoised against the store revision — it sits on the
publish path, so a dashboard slider was reading and validating every
flow file per value. Same mechanism `_wiring` already uses.
- the `message_value` source block is built once per node instead of per
emission.
- both timer threads ask the queue to promote only when something is
actually due, which takes an idle engine from ~4 Redis round trips a
second to one.
- the shared httpx client is bounded (32 connections, one retry); its
default pool is 100 with no per-host cap, so one slow endpoint could
take it and every other sender node with it.
- the MQTT and delay nodes no longer log a line per message at INFO.
Robustness, in the same pass:
- `MemoryWorkQueue._done` was a set nothing ever removed from — one entry
per non-idempotent node per item, for the life of the process, in the
default configuration. Capped, the way the Redis side expires its
markers.
- a saturated engine can claim from the due lane past the cascade limit.
The capacity gate sits in front of the claim, so the due lane's priority
— decided inside it — did not apply while every slot was held: a motor's
stop was not behind the long nodes, it was unread. Only after a slot has
genuinely failed to free for half a second, and briefly, so the backlog
is not starved in turn.
- `reclaim_stale` dispatches through that same gate. It could return sixty
entries and push in-flight far past the limit the gate exists to hold.
- a flow's nodes are stopped together rather than one after another. Each
gets `NODE_STOP_TIMEOUT`, so a flow whose broker was unreachable took
five seconds per node — long enough to outlast `REBUILD_WAIT` and 503
the deploy.
- the worker pool and the HTTP client are closed on a thread, not on the
event loop, and a run closes the state backend it built (on Redis, a
client and a connection pool per run).
- the five background tasks say something when they die. Each catches
exceptions inside its loop, so one raised anywhere else left the engine
serving with no metrics, no alerts or no artifact sweep, silently.
`tests/flow/test_round_trips.py` counts the state operations one message
costs — four, where it was about eleven — because none of the above would
fail a behavioural test if it were undone.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01M6hPWS6YEbT1P8LxhhFb2T
stroblmeandClaude Opus 5
da528340a9