Eclipse OpenJ9 user documentation

This documentation supports the configuration, tuning, and diagnosis of the OpenJ9 VM.

About this documentation

The Java virtual machine (VM) in IBM SDK®, Java™ Technology Edition was contributed to the Eclipse Foundation in 2017, forming the Eclipse OpenJ9 open source project. This material is based on the open source OpenJ9 documentation and should be used in conjunction with the IBM Semeru Runtime Certified Edition for z/OS, v17 user guide and J9 VM reference in IBM Documentation.

General notes on this documentation

• Some topics in this documentation are longer than a typical IBM Documentation topic page. For usability, we recommend enabling the full IBM Documentation Table of contents where additional entries are included to aid navigation. The Table of contents can be toggled on and off by using the arrow icon in the bottom-left corner of the screen, at the bottom of the side-bar.
• Because this documentation originates from the open source project there might be some references to features and settings that apply to later versions of Java SE. These references, which are typically marked with icons, should be ignored. For example, This sentence applies only to Java 20 or later runtime environments that include the OpenJ9 VM.
• Because this documentation originates from the open source project there might be some references to operating systems other than z/OS.
• Until the Eclipse Foundation have written a full set of user documentation for the OpenJ9 VM, some original IBM content is still provided in the J9 VM reference for completeness.
• The OpenJ9 documentation that is available on the Eclipse Foundation website might not match the functionality that is available in the current level of the SDK, and therefore should not be read.

Modifications to OpenJ9 behavior

The IBM SDK includes the OpenJ9 VM but modifies its behavior in a few cases. The differences between OpenJ9 in the IBM SDK and an unmodified OpenJ9 VM are already reflected in this documentation but are summarized here for reference:

Cryptographic operations

The IBM SDK contains the OpenJDK implementation of the TLS and SSL protocols, whereas OpenJ9 uses the OpenSSL open source library.