PostgreSQL Query Optimization: Reducing API Response Time from 2.8 Seconds to 74 Milliseconds

Short summary

A practical walkthrough of optimizing a slow PostgreSQL query that was causing 2.8s API responses on a 1.2M-row orders table. The root cause was a missing index on customer_id, causing sequential scans. Adding a composite index on (customer_id, created_at DESC) reduced response time to 74ms — a 38x improvement. The article covers EXPLAIN ANALYZE usage and index strategy.

• •Sequential scan on 1.2M-row table caused 2.8s API response times
• •Composite index on (customer_id, created_at DESC) cut response to 74ms — 38x faster
• •Covers EXPLAIN ANALYZE diagnosis, index strategy, and performance validation
• •Not AI-related but solid database optimization tutorial

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