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JEP 189 – Shenandoah: A Low-Pause-Time Garbage Collector (Experimental) Java 12 features

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RedHat initiated Shenandoah Garbage Collector to reduce GC pause times. The idea is to run GC concurrently with the running Java threads.

It aims at consistent and predictable short pauses irrelevant of the heap size. So it does not matter if the heap size is 15 MB or 15GB.

It is an experimental feature in Java 12

2. JEP 346 – Promptly Return Unused Committed Memory from G1

Stating Java 12, G1 will now check Java Heap memory during inactivity of application and return it to the operating system. This is a preemptive measure to conserve and use free memory.

3. JEP 344 : Abortable Mixed Collections for G1

Improvements in G1 efficiency include making G1 mixed collections abortable if they might exceed the defined pause target. This is done by splitting the mixed collection set into mandatory and optional.
Thus the G1 collector can prioritize on collecting the mandatory set first to meet the pause time goal.

4. JEP 230 and 344

Microbenchmark Suite, JEP 230 feature adds a basic suite of microbenchmarks to the JDK source code. This makes it easy for developers to run existing microbenchmarks and create new ones.

One AArch64 Port, Not Two, JEP 344, removes all of the sources related to the arm64 port while retaining the 32-bit ARM port and the 64-bit aarch64 port. This allows contributors to focus their efforts on a single 64-bit ARM implementation

5. JEP 341 Default CDS Archives

This enhances the JDK build process to generate a class data-sharing (CDS) archive, using the default class list, on 64-bit platforms. The goal is to improve startup time. From Java 12, CDS is by default ON.

To run your program with CDS turned off do the following:

java -Xshare:off HelloWorld.java

Now, this would delay the startup time of the program.


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