Performance Optimization

Introduction

Optimisation order matters: measure, then change. The 80/20 of Spring Boot perf is database, then JSON, then thread pools — almost never CPU-bound code.

Understanding the topic

The high-leverage list:

• 🐢 Slow DB queries — fix with indexes, projections, batch.
• 🔁 N+1 — join fetch / @EntityGraph.
• 📦 Connection pool too small (default 10) → tune to ~ 2 × cores or by load test.
• 🌐 HTTP timeouts — configure on every outbound client, never the default.
• 🧊 Cache hot reads in Redis with TTL.
• 🪶 JSON — use records, drop nulls, paginate.
• 🧵 Async + virtual threads for I/O-bound work (Java 21).