Node.js · Event Loop · Senior · Scenario
Scenario: API p99 latency jumps but CPU is low. Event loop related?
Short Interview Answer
Possibly event-loop delay from sync code bursts, UV thread-pool saturation, or lock contention — measure event loop lag.
Detailed Explanation
Instrument `monitorEventLoopDelay` / async hooks carefully. Check DNS, fs, and crypto pool sizes. Correlate with GC pauses. Low CPU with high latency often means waiting, not compute.