MaxMetaspaceSize

MaxMetaspaceSize is a Java Virtual Machine (JVM) option that limits the maximum amount of native memory that may be used for metaspace, the area that stores class metadata. Introduced in Java 8 as a replacement for PermGen, metaspace memory is allocated from native memory and is separate from the Java heap. Metaspace grows as new classes are loaded and can shrink when classloaders are garbage collected and classes are unloaded.

If MaxMetaspaceSize is not set, metaspace can grow dynamically up to the limits of the process and the operating system, potentially leading to OutOfMemoryError: Metaspace when memory is exhausted. Setting MaxMetaspaceSize provides an upper bound to prevent uncontrolled growth, which can be important in long-running applications or containerized environments.

Two related options control metaspace behavior. -XX:MetaspaceSize specifies the initial threshold for metaspace; when usage exceeds this value, the JVM triggers a garbage collection to reclaim unused metaspace before allowing further growth. -XX:MaxMetaspaceSize sets the hard ceiling for metaspace growth; attempting to allocate beyond this limit results in java.lang.OutOfMemoryError: Metaspace. Both values can be specified with units such as k, m, or g (for example, -XX:MaxMetaspaceSize=1g).

Practical tuning involves balancing memory footprint with class loading behavior. Metaspace usage can rise in environments with many dynamically loaded classes or frequent redeployments. Monitoring metaspace usage helps determine appropriate values, especially in constrained environments like containers.