NOTE
Diagnosing MySQL Production Problems
A symptom-first workflow for latency, CPU, I/O, locks, connections, replication, and query-plan regressions.
This is a historical learning note and may contain outdated or incomplete understanding.
Start from the user-visible symptom and time window, then correlate database metrics with workload changes. Check active connections/threads, query latency and errors, CPU, disk latency/IOPS, buffer-pool pressure, locks/deadlocks, redo/checkpoint state, and replica lag.
Use slow-query/performance-schema evidence to identify statement patterns and compare execution plans/cardinality estimates. Avoid making several tuning changes before establishing the bottleneck.