A logistics order service has run dual writes for three years

A medium Pipeline Design interview practice problem on DataDriven. Write and execute real pipeline design code with instant grading.

Domain

Pipeline Design

Difficulty

medium

Problem

A logistics order service has run dual writes for three years. The recon job catches 0.4% silent loss and 0.05% phantom events; notifications occasionally fire for orders that never shipped. The principal engineer is asked to replace the dual write with outbox plus CDC end to end without an outage. The section's four-step migration: shadow (dual-write plus outbox in parallel, compare counts), cutover (consumers read outbox-fed Kafka), verify (no drift), retire (recon job removed once drift stays clean). Walk the migration by composing the four steps, each with what runs in production at that step and the verification gate that lets the next step proceed.

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