PostgreSQL 10 High Performance - Third Edition

Query plan node structure

EXPLAIN output is organized into a series of plan nodes. At the lowest level, there are nodes that look at tables, scanning them, or looking things up with an index. Higher-level nodes take the output from the lower-level ones and operate on it. When you run EXPLAIN, each line in the output is a plan node.

Each node has several numeric measurements associated with it as well:

# EXPLAIN ANALYZE SELECT * FROM customers;
QUERY PLAN                                                   
----------
Seq Scan on customers  (cost=0.00..676.00 rows=20000 width=268) (actual time=0.011..34.489 rows=20000 loops=1)
Total runtime: 65.804 ms  

This plan has one node, a Seq Scan node. The first set of numbers reported are the plan estimates, which are the only things you see if you run ...