How to Correctly Read a PostgreSQL EXPLAIN ANALYZE Output

A slow query lands in your lap. You run EXPLAIN ANALYZE and get back a wall of indented text that looks like someone fed a query plan through a blender. Most developers stare at it for a few minutes and give up. You do not need to understand every node. There are five patterns that cover the vast majority of real-world slow queries, and once you can spot them, the output goes from intimidating to immediately actionable. Run it EXPLAIN ANALYZE SELECT u.name, COUNT(o.id) AS order_count FROM users u LEFT JOIN orders o ON o.user_id = u.id GROUP BY u.id, u.name ORDER BY order_count DESC LIMIT 10; Add BUFFERS to also see cache hit rates: EXPLAIN (ANALYZE, BUFFERS) SELECT ... Read the output The result is a tree of nodes, indented to show parent-child relationships. Each node performs one step of the query. The overall query is the root node; the deepest indented nodes run first. Limit (cost=1243.56..1243.58 rows=10 width=40) (actual time=48