Use This EXPLAIN Triage Deck Before You Tune
Recall the first diagnostic question to ask for common EXPLAIN symptoms.
What does a massive row-estimate mismatch usually tell you first? The planner is making decisions from a false belief about selectivity or distribution. Check statistics freshness, predicate shape, and skew before assuming a new index is the answer. A query ends with ORDER BY ... LIMIT 20 but still sorts a huge set. What two fix classes are you comparing? One changes the path, one changes the shape. Ask whether the query is broad because of access-path limits or because the shape stays too wide too long. The query is slow, so another index is always the safe first move.…
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