How would you improve the throughput of a FastAPI service?

Summary

Profile first, then: use async drivers end to end, avoid blocking calls in async def, reuse HTTP clients and DB pools, cache hot reads (Redis), offload heavy work to queues, optimize serialization, and scale workers horizontally.

Longer Answer

Common hotspots are DB queries (indexes, N+1), per-request client creation (create one httpx.AsyncClient in lifespan), and large Pydantic payloads (use response_model thoughtfully, ORJSON, or return pre-serialized data). Tune the DB pool against worker count so you don't exhaust Postgres connections (use PgBouncer). Load test with Locust/k6 and watch event loop lag.

Key Points

• No blocking calls in async paths
• Shared clients and pools via lifespan
• Cache + queue offloading
• Pool sizing vs DB connection limits
• Load test and measure event loop lag