Slow database queries are the #1 bottleneck in enterprise web applications. Learn how to interpret PostgreSQL EXPLAIN (ANALYZE, BUFFERS) execution plans, detect Sequential Table Scans, and design composite B-Tree indexes that eliminate disk I/O bottlenecks.
1. Interpreting PostgreSQL EXPLAIN (ANALYZE, BUFFERS)
-- Execute query plan with empirical timing & buffer hits
EXPLAIN (ANALYZE, BUFFERS, VERBOSE)
SELECT u.id, u.username, o.total_amount
FROM users u
JOIN orders o ON u.id = o.user_id
WHERE o.created_at >= '2026-01-01'
AND o.status = 'COMPLETED';2. Composite B-Tree Index Design
When indexing columns for multi-column WHERE clauses, order columns by equality first, followed by range predicates:
-- Optimal Index Placement: (status, created_at, user_id)
CREATE INDEX idx_orders_status_created_user
ON orders (status, created_at)
INCLUDE (user_id, total_amount);