How we migrated a live routing system using AI-assisted refactoring

Datadog's engineering team migrated their Stream Router service from a key-value FoundationDB model to a relational PostgreSQL/DuckDB architecture while serving live production traffic. The migration used Claude and Cursor in a test-driven loop: for each method, they provided the old implementation, new schema, and a failing test, letting AI generate a first pass while tests served as the correctness oracle. Key enablers were modular interfaces, a comprehensive end-to-end test suite, and a blue/green deployment setup that validated the new system against live traffic for weeks before cutover. Results were dramatic: operations that took 45 minutes now complete in ~1 second, the routing dataset shrank 40x, latencies dropped by orders of magnitude, and database costs fell 90%. The post is candid about AI limitations: it consistently produced correct but unoptimized SQL, requiring human input for batching, UNNEST tricks, and CTEs. The core lesson: the quality of your test suite is the ceiling for how much you can trust AI-generated code.

Source: https://www.datadoghq.com/blog/engineering/ai-assisted-storage-migration. 8 Sync News only summarizes and links out; content copyright belongs to the authors and original sources.