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Usually just before a Java release, I dedicate the newsletter to listing all the new performance features in the upcoming release and how to use them (I have done this every 6 months prior to each new release, you can track back to the previous February and August newsletters if you want to see what's new performance-wise in any particular release). This newsletter should be all about Java 23 performance features. However Java 23 has almost no significant changes that affect performance, so this will be a mixed newsletter with Java 23 items and items not specifically relevant to Java 23.

Java 23 does have some performance changes, these are listed in the news section below, but unless you are doing edge-case performance they are unlikely to affect you. Except for ZGC switching to generational GC mode as its default, which should be positive for any app using ZGC and indicates you should be turning on generational mode if you are on an earlier JDK and using ZGC.

Now on to the details of those Java 23 changes, as well as the relevant tools and other article links. And of course the tips from this month's articles, as ever, are extracted into this month's tips page.

A note from this newsletter's sponsor

News

Java performance tuning related news - Java 23 performance changes

• JEP-474 ZGC generational mode is now the default
• JDK-8329203 New Parallel GC Full GC algorithm - reduces footprint and performs better
• JDK-8320532 Thread.suspend/resume and ThreadGroup.suspend/resume are removed
• JDK-8319551 Resolution of the startup time regression with -XX:StartFlightRecording
• JDK-8330077 Add system property jdk.nio.file.WatchService.maxEventsPerPoll to set the maximum number of WatchService events before overflow
• JDK-8319251 Change LockingMode default from LM_LEGACY to LM_LIGHTWEIGHT - revert using -XX:LockingMode=1
• JDK-8139457 Relax alignment of array elements - improves the footprint in some cases, but Unsafe accesses to arrays could now be unaligned
• JDK-8325496 -XX:TrimNativeHeapInterval=ms is now an official product switch - allows the JVM to trim the native heap at periodic intervals
• JDK-8324066 clhsdb jstack no longer scans for java.util.concurrent locks by default - you need to use the -l option for that

Tools

Java performance tuning related tools

• jhsdb Java process and postmortem debugger
• -XX:TrimNativeHeapInterval=ms can be used in earlier JDK versions by adding add -XX:+UnlockExperimentalVMOptions, or dynamically applied with jcmd PID System.trim_native_heap
• WatchService for efficiently watching for file changes

Articles

• From Problem to Performance: A Case Study on Java Performance (Lennart ten Wolde/J-Spring)
• Mastering Java Performance: From Monitoring to Profiling (Lennart ten Wolde/J-Spring)
• Effective Performance Engineering at Twitter-Scale (Yao Yue/InfoQ)

Jack Shirazi

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