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May 6, 2026 · Backend Development

Spring Boot 4.1’s Default Virtual Threads Boost Throughput—But Require HikariCP Tuning

Spring Boot 4.1 makes virtual threads the default, dramatically increasing I/O concurrency, yet the unchanged HikariCP maximumPoolSize can exhaust connections; the article explains this incompatibility, shows how to adjust pool settings, enable lazy connections, and outlines a step‑by‑step migration path from 3.x to 4.1.