FastAPI insights
Open SourceVersions: [0.115]11 metricsWhen async endpoints make synchronous Redis calls, they hold connections longer than necessary while blocking the event loop, causing artificial connection pool exhaustion even when Redis server capacity is available.
Event loop blocking creates false appearance of cache ineffectiveness - Redis cache hits are fast individually, but serial request processing prevents concurrent cache lookups from improving overall throughput during traffic bursts.
When event loop blocking is the bottleneck, traditional infrastructure metrics (CPU, Redis ops, network I/O) appear healthy while request latency and timeouts increase - creating a diagnostic blind spot that delays root cause identification.
Without structured error tracking and categorization (4xx vs 5xx, error types), teams lack visibility into failure modes, making it difficult to distinguish client errors from server problems.