PostgreSQL Query Optimization: From Slow to Instant

A query that takes 4 seconds in development can take 40 seconds in production with real data. Understanding how PostgreSQL query planner works is not optional knowledge for developers.

Start with EXPLAIN ANALYZE. The difference between EXPLAIN and EXPLAIN ANALYZE is crucial: the former shows the plan; the latter executes the query and shows actual vs estimated row counts. Huge discrepancies indicate stale statistics.

Index selection matters more than most developers realize. A B-tree index on a Boolean column with 50% true/false distribution is nearly useless. Partial indexes, covering indexes, and expression indexes each have their place.