EXPLAIN

A conceptual walkthrough of what EXPLAIN actually does inside PostgreSQL - how the planner builds a plan tree, why ANALYZE changes the picture, and how to reason about the numbers you see.

Learn how EXPLAIN shows query access paths, including timing and buffer I/O with ANALYZE, BUFFERS, and other options in PostgreSQL.

Understand how PostgreSQL selects nested loop, hash, or merge joins based on row counts, memory, indexes, and sort order.

Understand how PostgreSQL handles sort and hash aggregates. Learn to identify and resolve performance issues when memory spills to disk.

Learn best practices for using EXPLAIN to triage slow PostgreSQL queries and approve index changes, including capture discipline and reading the EXPLAIN tree.

A single-page roundup of every highlight bullet from the 7 pages in the EXPLAIN section, grouped by source page so you can scan all 42 takeaways without opening each article individually.