JEP 387 “Elastic Metaspace” – a new classroom for the Java Virtual Machine
The Java Virtual Machine needs memory to breathe – sometimes more than we like. One of its hungrier subsystems can be the Metaspace, the part of the JVM holding class metadata. With JEP 387, SAP contributed a much more frugal and elastic implementation to the OpenJDK.
Java 16 came with a handful of new JEPs [1]. We find new features like the new Vector API and the now fully incubated Java Records. In this list, we also find the somewhat mysteriously named JEP 387: “Elastic Metaspace” [2]. Despite its relative obscurity, it was one of the largest outside contributions for this release, with the patch itself counting upwards of 25kloc.
Java – the Java Virtual Machine and the JDK – are developed under the umbrella of the OpenJDK [7], a massive Open Source project under the stewardship of Oracle and other companies. SAP has been a long-time contributor to that project, with our first involvement going back to 2012.
OpenJDK development is governed by processes, and normal enhancements go through a process called Request for Enhancement (RFE). An RFE requires patch reviews but usually little else unless the patch affects compatibility.
