Dependency Injection Graph Explosion
infolatencyUpdated Feb 6, 2026
Deep dependency trees in FastAPI dependency injection cause redundant validation and initialization overhead on every request, visible as pre-handler latency in traces.
Sources
How to detect:
Trace request timeline showing significant time (>20ms) spent before endpoint handler execution. Monitor dependency resolution depth and count. Track validation overhead in Pydantic models.
Recommended action:
Optimize dependency graphs by caching expensive dependencies at application startup. Flatten deeply nested dependency chains. Use FastAPI's dependency_overrides for testing without performance impact. Profile dependency injection overhead with detailed tracing.