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As usual just before each Java release, I'm listing all the new performance features in the upcoming release of Java 16 (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 release). As usual I give the new features, the performance benefits from each feature, and how to use the feature.

Java 16 has one big performance feature: similar to last month's announcement that Shenandoah should have no pauses over a millisecond in Java 17, ZGC has achieved the same fully concurrent status, but actually one release earlier! That's great, it means you can start testing straight away whether it works for you. As with Shenandoah, you'll need to have sufficient additional CPU and memory to achieve that performance. For small heaps (up to 1GB) or high throughput applications (ZGC and Shenandoah are targeting pauses, not throughput) it's likely that G1 is the better GC option (so good to see G1 features continued to be worked on, see JDK-8236926 below).

There are other performance features in this release: there's good news if you want minimal container footprint with the alpine port; if you need the fastest local inter-process communication we now have unix-domain socket channels (also works on Windows, MacOS, etc); Metaspace memory management is better; C++ support is upgraded; vector hardware support is testable; and Records are fully released - although not a direct performance improvement, this should improve the use of immutable objects and that will gradually feed in to better performance

Now on to the details of those Java 16 changes, including the options you have available to use them. 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 16 generally useful performance features.

• JEP376: ZGC: Concurrent Thread-Stack Processing. ZGC removed the last stop-the-world activity that takes variable time (this one was proportional to the number of threads), so should now be under a millisecond for all pauses (given sufficient memory and CPU available)
• JEP386: Alpine Linux Port. Alpine allows a smaller image than the other linux options, so smallest container size - under 50MB stripped JVM base image
• JEP380: Unix-Domain Socket Channels have been added (but not yet on Windows 2019 Server - https://bugs.openjdk.java.net/browse/JDK-8259014). For local, inter-process communication, Unix-domain sockets are both more secure and more efficient than TCP/IP loopback connections. Unix-domain sockets have faster setup times and higher data throughput than TCP/IP loopback connections
• Client-server example of using Unix-Domain Sockets
• JEP387: Elastic Metaspace - change the way metaspace is allocated and reclaimed to make it more efficient. An additional option is added -XX:MetaspaceReclaimPolicy=(balanced|aggressive|none). 'balanced' is default and should be similar but more efficient than previously ; 'aggressive' has better memory-reclamation rates at the cost of increased virtual-memory fragmentation; 'none' disables memory reclamation altogether.
• JDK-8236926: Concurrently Uncommit Memory in G1. This new feature is always enabled and changes the time when G1 returns Java heap memory to the operating system. G1 still makes sizing decisions during the GC pause, but offloads the expensive work to a thread running concurrently with the Java application

Java performance tuning related news - Java 16 niche but useful performance features.

• JEP347: Enable C++14 Language Features. If you use C++ with the JDK, you'll want to see whether the C++14 features can improve the performance or memory of your application
• JEP338: Vector API (Incubator). Vector computations that reliably compile at runtime to optimal vector hardware instructions. If you use these types of operations - eg ML, image processing, scientific processing, massive financial calculations, etc - then you should check it out and feedback since this matters to you
• JEP389: Foreign Linker API (Incubator). More flexible than JNI, and hopefully faster
• JEP393: Foreign-Memory Access API (Third Incubator). Further improvements due to feedback. Useful for off heap management
• Benchmark showing faster performance from the Foreign-Memory Access
• JEP395: Records. Likely to be faster than equivalent class objects, though probably in later JVMs after common usage is identified
• JDK-8247281: Object monitors no longer keep strong references to their associated object. Previously strong references would be observable through JVM TI functions that walk the heap (reported as JVMTI_HEAP_ROOT_MONITOR or JVMTI_HEAP_REFERENCE_MONITOR) and in heap dumps (reported as HPROF_GC_ROOT_MONITOR_USED). As of this release, a weak reference is used and these are not observable to JVM TI or heap dumps
• JDK-8255616: Removal of experimental features AOT jaotc and Graal JIT. Removed because it's used very little but has support cost. The sources for these features remain in the repository, in case any one else is interested in building them
• JDK-8256718: Old tracing flags are now obsolete and must be replaced with unified logging. Move: -XX:+TraceClassLoading to -Xlog:class+load=info ; -XX:+TraceClassUnloading to -Xlog:class+unload=info ; -XX:+TraceExceptions to -Xlog:exceptions=info ; -XX:+PrintSharedSpaces to -Xlog:cds=info
• JDK 16 G1/Parallel GC changes
• ZGC: What's new in JDK 16
• Metaspace in OpenJDK 16

Articles

• Metaspace in OpenJDK 16 (Leo Korinth/lkorinth)
• Talking to Postgres Through Java 16 Unix-Domain Socket Channels (Gunnar Morling/morling)
• JEP-380: Unix domain socket channels (Michael McMahon/Inside Java)
• Traffic Shedding, Rate Limiting, Backpressure, Oh My! How to stop your service from getting overloaded (Jack Shirazi/Expedia)

Jack Shirazi

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