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Java 12 is released in less than a month (on 19th March). I'm again listing all the new performance features, just as I now do every 6 months with each new Java version. The new features, the performance benefits from each feature, and how to use the feature.

As usual, for completeness, I'll also list the new features that have no performance effect so you have one place for reference. And of course the tips from this month's articles and talks are extracted into this month's tips page.

Before we go to the new features, I'll quickly mention my most recent article on optimizing your server by limiting request overheads that you might find interesting. And now those new Java 12 features ...

A note from this newsletter's sponsor

News

Java performance tuning related news - significant new performance features:

• Shenandoah low pause garbage collector added to the JVM. Use with -XX:+UnlockExperimentalVMOptions -XX:+UseShenandoahGC. They recommend also using -XX:+AlwaysPreTouch, -XX:+UseNUMA, -XX:+UseTransparentHugePages (and set /sys/kernel/mm/transparent_hugepage/enabled and /sys/kernel/mm/transparent_hugepage/defrag to "madvise" on Linux), -XX:-UseBiasedLocking and either -XX:+DisableExplicitGC or -XX:+ExplicitGCInvokesConcurrent
• a G1 improvement, no tuning options but a change in behaviour that means G1 can get more efficient over time based on runtime analysis - worth knowing about so that you let tests run long enough for heuristics to kick in, and so that if you are analysing you understand the behaviour
• G1 to return memory to the OS. Tuning options G1PeriodicGCInterval and G1PeriodicGCSystemLoadThreshold, 0 disables the features. If more than G1PeriodicGCInterval milliseconds have passed since any previous garbage collection pause and getloadavg() (one-minute) is below G1PeriodicGCSystemLoadThreshold then a full GC or concurrent GC (if G1PeriodicGCInvokesConcurrent is set) is triggered, and at the end of that GC the Java heap size is adjusted and any excess memory is returned to the operation system

Java performance tuning related news - new features with no performance impact:

• Add the Java Microbenchmark Harness JMH to the JDK
• Switch Expressions Preview
• New package java.lang.invoke.constant for describing loadable constants
• One AArch64 Port, Not Two

Tools

Java performance tuning related tools.

• Include a default class data-sharing (CDS) archive. This should help speed up startup. Xshare:auto was enabled by default in Java 11, but there was no default archive so each JVM needed to create one, this JEP adds a default. The JVM should start faster if there's already one (shareable) running. To turn off class data-sharing use -Xshare:off.
• Suggestions for performance analysing Shenandoah garbage collector
• Java Concurrency Stress test suite, jcstress, to aid testing the correctness of concurrency

Articles

• The Missing Benchmark Metric: Memory Consumption (Jens Wilke/FOSDEM)
• Exploring Java Heap Dumps (Ryan Cuprak/Devoxx)
• It Scales Until It Doesn't (Yaroslav Yermilov, Dmitry Tiagulskyi/Devoxx)
• Java Performance Testing for Everyone (Shelley Lambert/EclipseCon)

Jack Shirazi

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