PostgreSQL Index Fix Cuts API Response Time from 2.8 Seconds to 74 Milliseconds

A developer working on a Node.js and PostgreSQL application discovered that a customer orders API endpoint was taking 2.8 seconds to respond, making it unsuitable for production use. Investigation using PostgreSQL's EXPLAIN ANALYZE tool revealed the database was performing a full sequential scan across a table of over 1.2 million rows on every request. The root cause was the absence of an index on the customer_id column, forcing PostgreSQL to read and filter large portions of the table for each query. Adding a single-column index on customer_id, followed by a composite index on both customer_id and created_at, eliminated the sequential scan and enabled efficient index-based lookups. The optimizations reduced average response time from 2.8 seconds to 74 milliseconds, a roughly 97% improvement and approximately 38 times faster performance.