Why MySQL JDBC Stalls on Java Virtual Threads—and What to Do

MySQL’s JDBC driver has been the last major driver to fully support Java’s virtual threads (Project Loom), causing compatibility issues for developers using JDK 21.

Oracle’s JDBC driver (ojdbc11.jar and later) already supports virtual threads, as confirmed on the official Oracle JDBC page

https://www.oracle.com/cn/database/technologies/appdev/jdbc.html

. PostgreSQL’s driver also added support early on, and both MariaDB Connector/J and Microsoft SQL Server JDBC driver have been updated to work with Loom.

In contrast, MySQL’s driver lagged behind, only achieving complete virtual‑thread support in the 9.x series after a prolonged delay. The earlier versions used synchronized heavily, which pins virtual threads during JDBC calls and degrades performance.

One practical workaround is to replace the synchronized blocks with ReentrantLock, which eliminates the pinning problem. The change was finally incorporated in the 9.x driver release.

Even though JDK 24 (JEP 491) introduces optimizations for synchronized, upgrading the driver to the 9.x version remains the safest approach.

Beyond virtual‑thread support, upgrading the JDK is advisable because Java 8 stopped receiving public updates in 2019, raising security risks. Moving to a newer Java version improves both performance and security.