JProfiler Get rid of your performance problems and memory leaks! Modern Garbage Collection Tuning Java Performance Training Courses COURSES AVAILABLE NOW. We can provide training courses to handle all your Java performance needs Java Performance Tuning, 2nd ed The classic and most comprehensive book on tuning Java Java Performance Tuning Newsletter Your source of Java performance news. Subscribe now! Enter email: Training online Threading Essentials course JProfiler Get rid of your performance problems and memory leaks!

Back to newsletter 226 contents

Pop quiz: how many different garbage collectors are available for you to use in OpenJDK Java 11+? For example the G1 collector is one garbage collector, and the Serial collector is another. I'm not talking about the copying collectors in the young gen and the others in the old gen, because these are all coupled together now forming a single multi-gen collector - earlier versions of Java did allow you to mix and match some of the young gen and old gen algorithms, but that is no longer possible and choosing a collector now chooses the algorithm for all gens. Stop reading now so you can properly think it through, and answer the quiz, I am willing to bet you'll get it wrong (unless you've already seen the answer after this newsletter goes live and everyone popularizes it).

The answer is 12. This isn't some subtle trick, some hidden way of multiplying the collectors. There are 2 JVM implementations in the OpenJDK - HotSpot and OpenJ9. HotSpot has 7 collectors available and OpenJ9 has 6. That would total 13, but one of the collectors (Epsilon) is the same collector in both, resulting in 12 collectors.

The full list:

• Both: Epsilon -XX:+UseEpsilonGC and -Xgcpolicy:nogc
• HotSpot: Serial -XX:+UseSerialGC; Parallel -XX:+UseParallelGC; CMS -XX:+UseConcMarkSweepGC; G1 -XX:+UseG1GC; ZGC -XX:+UseZGC; Shenandoah -XX:+UseShenandoahGC
• OpenJ9: Balanced -Xgcpolicy:balanced; Concurrent -Xgcpolicy:gencon; Metronome -Xgcpolicy:metronome; Pause time -Xgcpolicy:optavgpause; Throughput -Xgcpolicy:optthruput

Now on to this month's tips, tools, news, articles, and those talks. And of course the tips from this month's articles and talks, as ever are extracted into this month's tips page.

A note from this newsletter's sponsor

News

Java performance tuning related news.

• Details on the proposed Vectorization API that lets you optmize parallel calculations for the CPU architecture. Can be used now if you need speedups, but a few years away from mainstream release
• Comparing the performance of different JVMs including JDK 8 and JDK 11 and HotSpot, OpenJ9 and GraalVM
• Top4j lightweight open source performance analysis tool for Java released
• Tascalate Concurrent - Filling the Gaps in CompletableFuture API

Tools

Java performance tuning related tools.

• Many low level libraries including Off Heap Memory Access; JVM Access Methods; OS Calls; Resource Reference Counting; Object Pools; Class Local Caching; Maths Functions for casting types, rounding double, faster hashing; Serializable Lambdas
• Top4J is a lightweight, low overhead, production-ready performance analysis tool for the Java runtime environment
• Library augmenting CompletableFuture, providing an implementation of the CompletionStage interface and related classes to support long-running blocking tasks (typically, I/O bound)
• Processor Counter Monitor (PCM) is an application programming interface and a set of tools based on the API to monitor performance and energy metrics

Articles

• Hunting Down Scalability Bottlenecks in Java (Sergey Kuksenko/Oracle CodeONE)
• Monitoring and Troubleshooting Tools in JDK/bin (Poonam Parhar/Oracle CodeONE)
• Monica-Beckwith-on-Java-Garbage-Collection (Monica Beckwith/ieeeComputerSociety)
• Java Concurrency, A(nother) Peek Under the Hood (David Buck/Oracle CodeONE)

Jack Shirazi

Back to newsletter 226 contents