Introduction to Using the EXPLAIN Command in PostgreSQL

This text introduces the concept of PostgreSQL query planning, explaining how databases store information in heaps and how the database engine accesses these pages on the disk or cache to retrieve relevant information. The article then delves into how PostgreSQL processes queries, including parsing and preliminary processing, creating a query plan, and executing the query plan. It also explains how query execution works, with each node in the query plan tree returning a set of rows. The text further discusses EXPLAIN commands used to know details about the execution path (query plan) and optionally, the execution time and other operational details. It introduces table statistics and vacuuming operations that help Postgres estimate execution times and choose the most efficient execution path. The article concludes by explaining how to run the EXPLAIN commands using either the PSQL interface or the pgAdmin 4 GUI Query Tool.