PostgreSQL Plan Signatures: Quick Reference A scannable lookup companion to the Complete Guide to PostgreSQL SQL Query Analysis & Optimization series. Designed for when you have an EXPLAIN plan in front of you and need the pattern → fix mapping fast, without re-reading the deep-dive articles. Three tables below: Plan-node signatures — "when you see this, do that." SQL anti-patterns — "if your code looks like this, replace with that." MyDBA analyzer rules — severity, trigger condition, and the article that covers each. If a row points to a deeper article, that's where the full explanation with captured EXPLAIN examples lives. 1. Plan-node signatures A "signature" is a field or combination of fields you can spot in an EXPLAIN plan at a glance. Plan signature What it means Fix Deep dive Seq Scan on table > 10k rows with selective filter Missing or unusable index Add an index on the filter column, or see non-sargable cases below Index usage Seq Scan + Filter: fn(col) = ...…