HikariCP Connection Pool Tuning for Production

The Pool Size Formula

HikariCP recommends: *pool_size = (cores 2) + effective_spindle_count**

For a 4-core machine with SSD: pool_size = (4 * 2) + 1 = 9

spring:
  datasource:
    hikari:
      maximum-pool-size: 10
      minimum-idle: 5
      connection-timeout: 30000      # 30s — fail fast
      idle-timeout: 600000           # 10min
      max-lifetime: 1800000          # 30min (less than DB wait_timeout)
      keepalive-time: 30000          # prevent firewall drops
      leak-detection-threshold: 60000 # detect connection leaks

Diagnosing Connection Leaks

Enable leak detection and check logs for:

WARN  c.z.h.p.ProxyLeakTask - Connection leak detection triggered

Common causes: missing try-with-resources, exceptions bypassing close(), @Transactional on too-coarse methods.

Interview Questions

1. 1.Why should max-lifetime be less than the database's wait_timeout?
2. 2.What is the difference between connectionTimeout and socketTimeout?
3. 3.How do you size a connection pool when using virtual threads?
4. 4.What metrics should you alert on for connection pool health?