Thread pool deadlock under load
v33 of a Java service deploys at 08:30. Under normal load it works, but during the morning traffic ramp at 09:15 it locks up: requests hang indefinitely, the service's health check still returns 200, but no requests complete and CPU drops to near zero. A thread dump shows all threads in a fixed-size thread pool BLOCKED, and many are waiting to submit work to that same pool. v33 introduced a pattern where a request task, running on the pool, synchronously submits a sub-task to the same bounded pool and waits for its result. Triage and mitigate.
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 40 min
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.