jvm-memory

2 Posts

Java Object Header: Mark Word, Class Pointer and Layout

What's in a Java object header? Mark word, class pointer and padding, measured with Unsafe on JDK 21, plus what compact headers change in JDK 25.

Java Heap Size in Containers: -Xmx vs MaxRAMPercentage

Java heap size in a container isn't what -Xmx says. How the JVM derives it from the cgroup limit, why 75% heaps still get OOMKilled, and how to budget the rest.