Permgen elimination in JDK 8

java

jvm-tuning

memory-management

gc-performance

byAlex Kataev·Dec 10, 2024

JDK 8 replaces the PermGen space with the Metaspace. Metaspace scales up dynamically, leveraging native memory for class metadata. Manage its size by setting -XX:MetaspaceSize for initial allocation and -XX:MaxMetaspaceSize to limit growth:

// Setting the initial and maximum metaspace size - Because who doesn't like control? 😉
-XX:MetaspaceSize=256m -XX:MaxMetaspaceSize=1g

Adapt these parameters to suit your application's requirements for optimal performance.

Note: Disregard any warnings regarding MaxPermSize when running applications such as Eclipse on JDK 8. The removal of the MaxPermSize option is by design.

Metaspace Mechanism and Management // changed heading

Metaspace - The Hero we Needed

Metaspace overcomes several PermGen hitches. It doesn't require GC (Garbage Collector) scanning or compaction, which enhances overall GC performance. Metaspace allotment is linear for improved efficiency and utilizes native memory that skirts java.lang.OutOfMemoryError: PermGen situations. Unlike the fixed-cap PermGen, Metaspace has no hard upper limit and can grow as per your application's needs.

Tuning Metaspace - Power to You!

As Spiderman's Uncle Ben says, "With great power comes great responsibility." So with Metaspace's elasticity, it's crucial to supervise its growth. Set a sensible size as its initial limit using -XX:MetaspaceSize and cap it with -XX:MaxMetaspaceSize as necessary to avoid swallowing up system memory. Knowledge of Metaspace's workings proves beneficial in crafting effective JVM tuning strategies and staying in Uncle Ben's good books.

The Future is Now // changed heading

Diskarding PermGen opens up opportunities for future JVM optimizations and feature introductions. The change simplifies potential advancements in the realm of memory management strategies.

Diving Deeper – PermGen vs. Metaspace // changed heading

Wisdom Gleaned from JEP 122

Delve into the motivating factors behind PermGen’s extermination in JEP 122. The PermGen space was the root cause of several complications including, but not limited to, memory leaks and convoluted JVM tuning demands. The migration to Metaspace simplifies both the Java developer's coding journey and enhances JVM's memory management.

Alternate JVM Tuning Opportunities

Wrap your head around other JVM tuning options that JDK 8 offers, with the aid of other JEPs. A quick investigation of the JDK 8 milestones page will guide you to a list of these performance-enhancing JEPs.