Outbox Pattern Prevents Stale Notifications by Re-Checking Conditions Before Sending

A developer building a price-watcher app on Cloudflare Workers and D1 identified a reliability problem: notifications sent immediately upon detecting a trigger condition can become outdated within seconds or minutes. To fix this, they implemented the outbox pattern, where detection only writes a row to a database table and a separate process handles actual delivery. Before sending, the system re-fetches the current value and confirms the original condition still holds, dropping the notification if it no longer applies. Duplicate alerts are suppressed using a unique SQLite index that collapses repeated triggers for the same item on the same day into a single row. The approach uses a simple state machine with statuses like pending, sending, sent, dropped, and failed to ensure each notification is processed exactly once and only when still relevant.