HikariCP: the p95 that lies to you and how to read the real pool signals There was a version of this analysis that started wrong. I was looking at the p95 for the tiny scenario with a 500ms delay and seeing 260.78ms . Compared to the default scenario showing 2418.16ms , it looked almost five times faster. That's a classic trap, and I almost fell for it. The tiny scenario had a 97.05% error rate. Out of 8139 attempts, 7899 failed. Those 260ms were the average rejection time, not the time for a useful response. It wasn't fast — it was failing fast. And that difference matters enormously when you're trying to understand whether your HikariCP configuration is working or not. That led me to build hikaricp-pool-experiment : a reproducible lab with Java 21, Spring Boot 3.4.5, PostgreSQL 16, HikariCP, Docker Compose, and k6 0.51.0. The goal wasn't to simulate production or document a real incident.…