How to Troubleshoot and Optimize Slow PostgreSQL Queries: A Practical Tutorial from EXPLAIN to Index Rebuilding

When many backend developers encounter slow API endpoints, their first reaction is to add more servers. In reality, most issues originate from the SQL itself. A while ago, while working on a B2B SaaS project in the U.S., I handled an order list endpoint where the p95 latency dropped from 3.8 seconds to 220 milliseconds. What really worked wasn't 'voodoo' parameter tuning, but systematically…