IBM has introduced free of charge Semeru runtime which use the OpenJDK class libraries with Eclipse OpenJ9 Java Virtual Machine (JVM). Runtimes, based on OpenJ9, can be used as an alternative to runtimes based on Hotspot. Previously, AdoptOpenJDK binary products with OpenJ9, but this is no longer legally allowed since their go to the Eclipse Foundation under the new name, Adopted.
IBM provides Java 8, 11 and 16 based Semeru Runtimes for Linux, Windows, macOS and AIX as well as various architectures. Docker images will be soon to follow. Two versions are available: an open edition with a GPLv2 + Classpath open source extension license and a certified edition with an IBM license. Both versions pass the Eclipse AQAvit test suite and certified edition is TCK-certified too. The Certified Edition replaces the older version of IBM SDK Java Technology Edition 11. There are no restrictions on use and runtimes can be used anywhere from development to production. IBM offers optional commercial support through IBM Runtime for Business.
The performance overview created by Eclipse OpenJ9 project compares OpenJ9 and Hotspot VMs for OpenJDK 11. OpenJ9 starts about twice as fast due to shared class cache and early compilation (AOT). After startup and while charging, the footprint is several tens of percentages smaller than Hotspot. Finally, peak throughput is achieved faster with OpenJ9, although Hotspot has higher throughput in the long run. OpenJ9 also has similar advantages when used with Quarkus.
Recent versions of OpenJ9 introduced improvements for execution inside containers. One of them is the
-XX:+ClassRelationshipVerifier command line option for lazily checking class relations, because some classes are never loaded. This improves start-up times. Shared Class Cache (SCC) is used to cache Java classes, AOT compiled code, etc. The cache persists even after shutting down the JVM to ensure continued boot performance the next time information is loaded from memory instead of disk. OpenJ9 testing shows that these improvements translate to a 45% faster boot time when comparing OpenJ9 with HotSpot.
At JavaOne 2016, Jean Duimovich, then Java CTO at IBM, announced their Java J9 virtual machine would be open source and given at the Eclipse Foundation. IBM has continued to work on OpenJ9 since then. IBM WebSphere Freedom and WebSphere application server will also use Semeru Runtimes.
More information is available in the to start to guide.