Our P95 spiked, now what?

Yesterday one of our Application Insights dashboard showed a P95 latency spike and we had no idea why. The telemetry told us that a request was slow. But it didn't tell us why . Was it a database call? A CPU-bound loop? Lock contention? A GC pause? The naive approach would have to been to add logging statements around the code you suspect, redeploy, wait for the issue to reproduce, and repeat. In…