fastapi-async-patterns

Prevent event-loop blocking during SSE streaming by using httpx async streaming to forward upstream chunks directly, avoiding synchronous decode or buffering pitfalls that collapse throughput. This ensures non-blocking proxy behavior under load.

FastAPI lifespan management creates and correctly disposes shared async resources like httpx clients and SQLAlchemy async engines or session factories during application startup and shutdown. This guarantees proper client and session lifecycle management.

Manage async DB sessions and concurrency control by injecting request-scoped sessions via Depends, defining transaction boundaries with session.begin(), and applying load-shedding using asyncio.Semaphore for safe task and session boundaries.

Yes, you can execute fire-and-forget background tasks in FastAPI by having those tasks open their own independent async SQLAlchemy sessions. This maintains safe task and session boundaries without blocking the main event loop.

Mixing synchronous code with FastAPI async patterns causes production failures because synchronous operations block the asyncio event loop. Using async-only libraries for httpx streaming and SQLAlchemy async sessions ensures non-blocking throughput.