Walk a Slow Query From Symptom to Fix
Diagnose a slow query by moving from user symptom to plan evidence before changing indexes.
Production symptom Customers page alternates between 120 ms and 9 seconds during sales-demo hour. Intermittent database slowness usually means parameter shape, lock waits, cache state, or plan choice. Guessing from the endpoint name is not evidence. EXPLAIN discipline Scope -> Plan -> Cardinality -> Smallest fix The goal is to identify the expensive mechanism before adding weight to the database. Reflex Add an index on the first column mentioned. A fix tied to the observed bottleneck, not a hopeful tuning change. Plans are explanations of work. Treat each step as a hypothesis about rows and cost. Scope the symptom First…
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