Read a query plan, add the right index, and turn slow queries fast — without guessing.
Web DevelopmentPDF · 5 pages· v1.0
4.7Your query is slow. Someone says 'add an index.' You add one and nothing changes. This guide is for that moment. It teaches application developers — not database administrators — how PostgreSQL indexes actually work, how to read EXPLAIN ANALYZE output well enough to know what is slow and why, and how to choose the right index for the query you have. It covers B-tree, multicolumn, partial, and expression indexes, plus when an index will not help at all. Every concept is grounded in a real query and its plan. You will learn why column order in a multicolumn index matters, why a function in your WHERE clause defeats a normal index (and how an expression index fixes it), why low-selectivity columns are not worth indexing, and the real cost indexes add to writes. After reading you will be able to take a slow endpoint, run EXPLAIN ANALYZE, identify whether it is doing a sequential scan it should not be, add a targeted index, and confirm the plan changed. You will also stop adding indexes that do nothing but slow down your inserts. Who it is for: backend and full-stack developers who write SQL or use an ORM against PostgreSQL and want their slow queries to actually get faster.
No. It is written for application developers. It assumes you can write a basic SQL SELECT and explains everything about indexes and query plans from there.
Yes. The ORM generates SQL that runs the same way. The guide shows how to capture the generated query and run EXPLAIN ANALYZE on it.
The concepts apply to all currently supported versions (13 through 17). Nothing relies on a version-specific feature.
No, and the guide explains why. Indexes speed up reads but slow down writes and use storage. It shows how to pick only the ones that earn their keep.
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