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Java 11 is released in a month (on 25th Sep). It seems like only 6 months ago that I listed all the Java 10 performance features, and of course that's because it was only 6 months ago - that's the new release cadence for Java. Regardless of other aspects, the new cadence and communications is great for manageably understanding the new features that we're getting. So naturally, just as I did 6 months ago for Java 10, this month I'm again listing all the new performance features and how to use them, for Java 11. All of our regular sections, tools, news, and articles/blogs/talks are focused on Java 11 related features, starting with the news section listing every significant new feature in Java 11, the performance benefits from that feature, and how to use the feature.

Now on to all those sections, but first I'll mention the most important performance item in Java 11 - one that is not listed: The CMS GC is still there! Despite the insistence of many a commentator that CMS would be gone in Java 11, it is still there, which will come as a huge sigh of relief for many many companies who were not yet seeing adequate enough performance from G1.

And of course the tips from this month's articles and talks, are extracted into this month's tips page.

A note from this newsletter's sponsor

News

Java performance tuning related news - significant new performance features:

• Many many improvements in G1 mean that if you are using G1 and it's not quite meeting your targets, you should try out the Java 11 JVM on your existing application to see if you get an immediate garbage collection improvement
• JEP 331: Low-Overhead Heap Profiling - low-overhead enough (less than 3%, maybe even less than 1%) to be enabled by default, letting you continuously sample Java heap allocations. Accessible via JVMTI. I expect there will be profilers available to use this as soon as it is released. Potentially the single biggest improvement here - low overhead simple object profiling in production
• JEP 318: Epsilon: A No-Op Garbage Collector - using a new flag -XX:+UseEpsilonGC or -XX:+UseNoGC, this new GC allocates but doesn't collect; once the heap is full the JVM will shut down. Useful for testing and specialized applications that never need a GC (using this collector would avoid GC barriers that are added to the application by other collectors even when no collection is triggered, so if you need to eliminate every last bit of overhead as in ultra-low latency applications, it's a valid GC option)
• JEP 328: Flight Recorder - now open sourced and added in Java 11, records events originating from applications, the JVM and the OS targeting less than 1% overhead when enabled and no overhead when not enabled. Turn on with -XX:StartFlightRecording or dynamically using jcmd with options JFR.start, JFR.dump filename=recording.jfr JFR.stop (eg jcmd PID JFR.start). jdk.jfr package let's your application create events, and also process recorded files of events. Expect this to become pretty standard now that it's open sourced, you should learn to use this if you currently don't - see this month's articles and tools sections for details
• JEP 321: HTTP Client (Standard) - Expected to enable better asynchronous handling of HTTP requests with fewer resources required, using the java.net.http package. You're probably using an Apache or other package which already does this anyway, but whatev, better late than never
• JEP 333: ZGC: A Scalable Low-Latency Garbage Collector (Experimental) - new collector targeting pauses of under 10 millisecond for any size heap. ZGC is a concurrent, single-generation, region-based, NUMA-aware, compacting collector; Stop-the-world phases are limited to root scanning so pretty quick! Experimental - need to compile a JVM with --with-jvm-features=zgc and then enable with -XX:+UnlockExperimentalVMOptions -XX:+UseZGC. Likely to require much more memory and CPU than other existing openJDK collectors
• JEP 309: Dynamic Class-File Constants - unlikely to be any immediate performance change (not many tools can take advantage of it yet), though longer term it might reduce startup time by having some processing moved to compile-time and lazy loaded. May be useful for specialized applications that want to use Epsilon (the no-op GC) as it might eliminate some object creation. The new java.lang.invoke.ConstantBootstraps class is provided to assist Java implementations using this feature
• CONSTANT Dynamic with Dan Heidinga and Paul Sandoz Jul 30, 2018 - as an example of how this can improve resource usage, anything that you would make static final but may never use, you can instead put in the constant pool and it only gets loaded if you use it
• Rafael Winterhalter provides a more detailed explanation of constant dynamic and adds an example of using it

Java performance tuning related news - minor new performance features:

• JEP 315: Improve Aarch64 Intrinsics - improves performance of sin/cos/log functions on some ARM64 processors
• JEP 324: Key Agreement with Curve25519 and Curve448 - small performance improvement expected in some cryptography functions
• JEP 332: Transport Layer Security (TLS) 1.3 - small performance improvement expected
• JEP 181: Nest-Based Access Control - unlikely to be any performance change (theoretically there could be a benefit from direct access of fields without bridge methods, but in practice the JIT already inlines those)

Java performance tuning related news - the remaining new features in Java 11 have no expected performance benefit but are also not expected to cause any negative performance impact, and are listed here just for completeness of feature listing:

• JEP 323: Local-Variable Syntax for Lambda Parameters
• JEP 327: Unicode 10 [emojis!]
• JEP 329: ChaCha20 and Poly1305 Cryptographic Algorithms
• JEP 330: Launch Single-File Source-Code Programs
• JEP 335: Deprecate the Nashorn JavaScript Engine
• JEP 336: Deprecate the Pack200 Tools and API
• JEP 320: Remove the Java EE and CORBA Modules
• APIs to be removed from Java 11

Tools

Java performance tuning related tools.

• Java Flight Recorder Command Reference
• Java Flight Recorder Runtime Guide
• How to Produce a Flight Recording
• Using Java Flight Recorder
• Java Mission Control User's Guide

Articles

• Java Flight Recorder (JFR) (Daniel Shaya/Rational Java)
• Java 11 Features - Java Flight Recorder (Siva Prasad Rao Janapati/smarttechie)
• Using Java Flight Recorder (Marcus Hirt/Parleys)

Jack Shirazi

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