Postgres Indexing That Actually Moves Latency

Measure first

“Add indexes everywhere” was worse than waiting for slow query logs. Index on paths you actually filter and join.

High-value patterns

• Foreign keys used in JOIN and WHERE
• Composite indexes matching common filters, e.g. (user_id, created_at DESC)
• Avoid low-selectivity single-column indexes that never get used

After adding an index

1. EXPLAIN (ANALYZE, BUFFERS) the slow query
2. Watch write amplification on insert-heavy tables
3. Drop unused indexes later — they are not free

Index the query, not the table.