Walk me through reading an EXPLAIN ANALYZE plan to find why a query is slow.
The reflex is 'add an index,' but a good engineer reads the plan before touching anything. The signal is spotting the operator that dominates runtime, comparing estimated against actual rows, and knowing the seq-scan, bad-join, and spill patterns.
Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.
The reflex is 'add an index,' but a good engineer reads the plan before touching anything. The signal is spotting the operator that dominates runtime, comparing estimated against actual rows, and knowing the seq-scan, bad-join, and spill patterns.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.
