#race-condition

Crypto Trading Systems Bug Report

Order state machine crashes with unknown order: the fill arrived before the REST response

Ryan Pham · Sep 16, 2026 · 6 min read

Our order manager occasionally raised KeyError: unknown order when a fill event arrived on the websocket before the REST place-order call returned. It keyed orders by exchange order id, which it only learned from the REST response. Keying by client order id and buffering unknown events fixed it.

Databases Bug Report

100 rare items, 140 players got one: a read-then-write race when thousands claimed at once

Le Minh Khoa · Nov 6, 2025 · 7 min read

Our game released 100 limited items at 20:00, and about 20,000 players tapped claim within seconds. 140 players received one. The endpoint checked remaining stock, then decremented it separately. How we proved the race and fixed it with an atomic conditional update, a constraint and a Redis gate.