Imagine your current production application starts timing out intermittently on a key user flow that spans frontend, API, and database. You have only basic logs and no detailed tracing tools. How would you systematically narrow down the root cause across the stack?

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VirtualInterview.AI · Accepted Answer

I’d treat it like a controlled investigation and work front-to-back. First, I’d quantify the impact: which endpoint, which user segment, what time ranges. Even with basic logs, I can usually correlate spikes in latency with specific routes or queries and see if timeouts align with traffic peaks or particular tenants.

From the frontend, I’d use the browser’s network panel and simple timing markers to see if delays are in rendering, network, or response time. Then I’d hit the same flow via cURL/Postman from a stable network to isolate frontend vs backend.

On the API side, I’d temporarily add lightweight timing logs around external calls and DB access, plus correlation IDs. For the database, I’d enable slow query logs and check locks, missing indexes, or queue build-up. In a recent case, this approach surfaced a single unindexed report query that caused p95 latency to jump from 600ms to 9s under load; adding the right index and a read replica dropped timeouts to effectively zero.

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