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A report query that used to finish quickly has become noticeably slower as one of our PostgreSQL tables has grown. The query filters on a date range and joins two related tables; it hasn’t changed, but the data volume has.
What would you inspect first to tell whether this is an indexing problem, a query-plan change, or something else? I’m trying to understand how to read PostgreSQL query plans when the same query behaves differently at different table sizes.
