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Code RoomQueue depth increases tail latency
HardPrep Room Coding #2612

Queue depth increases tail latency

On-callReliability & on-callSenior–Staff~35 min

During traffic surges your service's p99 balloons to 4-6s while p50 stays low, and notably the very old requests are the ones timing out — by the time the server starts processing a request, the client has already given up. You recently raised the inbound accept/request queue depth and the worker queue size 'so we stop dropping requests under load.' CPU is at 100% during the surge but throughput (completed RPS) actually fell vs. before the change. How do you triage and fix?

What a strong answer looks like

Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.

0:00 of about 35 min
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