The 185-Microsecond Type Hint

3 hours ago

A 'trivial' change in code yielded a 13× throughput increase in a Clojure Roughtime implementation.
The Roughtime protocol involves cryptographic proof for secure time synchronization, where servers respond with signed certificates containing nonces and timestamps.
The server's heavy lifting includes queueing, protocol compatibility across 16 versions, recursive Merkle tree hashing, and Ed25519 signatures.
Initial benchmarks showed 200µs response time, with 90% runtime attributed to a simple line calculating byte array lengths.
Adding a type hint to the `alength` function reduced encoding time from 31µs to 4µs by avoiding dynamic dispatch and reflection.
End-to-end benchmarks showed throughput increased from 19,959 to 264,316 responses per second, a 13× improvement.
The unexpected speedup may be due to reduced contention in reflective call paths under load.
The lesson: even 'trivial' code can be a bottleneck, and type hints can significantly optimize performance in Clojure.

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