How do you know you need a database index?

Short summary

Learn a framework for identifying database columns that need indexes by examining WHERE, ORDER BY, JOIN, and GROUP BY clauses, then proving the benefit with EXPLAIN ANALYZE and measuring real write costs before committing. Foreign keys and lookup columns are the easiest wins; composite indexes with the most selective filter first yield the best performance-to-cost ratio. Index strategically based on production query logs and pg_stat_statements, not hunches — unused indexes are pure cost with no upside.

• •Index columns in WHERE, ORDER BY, JOIN, GROUP BY clauses only if the table is large or growing
• •Use EXPLAIN ANALYZE before/after to prove impact; check production with pg_stat_statements, not local development
• •Add indexes only for queries you can show are expensive; unused indexes slow writes with no benefit

Generated with AI, which can make mistakes.