PostgreSQL: Up and Running, 3rd Edition

Chapter 9. Query Performance Tuning

Sooner or later, we’ll all face a query that takes just a bit longer to execute than we have patience for. The best and easiest fix is to perfect the underlying SQL, followed by adding indexes and updating planner statistics. To guide you in these pursuits, PostgreSQL comes with a built-in explainer that tells you how the query planner is going to execute your SQL. Armed with your knack for writing flawless SQL, your instinct to sniff out useful indexes, and the insight of the explainer, you should have no trouble getting your queries to run as fast as your hardware budget will allow.

EXPLAIN

The easiest tools for targeting query performance problems are the EXPLAIN and EXPLAIN (ANALYZE) commands. EXPLAIN has been around since the early years of PostgreSQL. Over time the command has matured into a full-blown tool capable of reporting highly detailed information about the query execution. Along the way, it added more output formats. EXPLAIN can even dump the output to XML, JSON, or YAML.

Perhaps the most exciting enhancement for the casual user came several years back when pgAdmin introduced graphical explain. With a hard and long stare, you can identify where the bottlenecks are in your query, which tables are missing indexes, and whether the path of execution took an unexpected turn.

EXPLAIN Options

To use the nongraphical version of EXPLAIN, simply preface your SQL with the word EXPLAIN, qualified by some optional arguments:

• EXPLAIN by itself will ...