Collector Combinations: Serial, Parallel, Concurrent, G1, Z

This section describes different garbage collector combinations supported by JVM 12 HotSpot: Serial, Parallel, Concurrent, G1 and Z

In previous sections, we discussed garbage collectors for Young generation and Tenured generation independently:

A single generation collector, called Z (or ZGC) The Z collector has been introduced since JVM 11 and it is still available only on Linux operating systems as an experimental option. The Z (or ZGC) Collector can be invoked by the "-XX:+UseZGC" option.

Now let's look dependencies and compatibilities of garbage collectors. As of JVM 12, HotSpot JVM can support the following 5 combinations of garbage collectors:

GC Combination           Minor GC          Major GC            Thread
--------------           --------          -------            ------

Serial                   Serial            Serial             1
-XX:+UseSerialGC         Stop-the-world    Stop-the-world

Parallel                 Parallel Scavenge Parallel Old
-XX:+UseParallelGC       Mostly Parallel   Mostly Parallel    Multi
-XX:+UseParallelOldGC    Stop-the-world    Stop-the-world

Concurrent               Parallel New      CMS
-XX:+UseConcMarkSweepGC  Mostly Parallel   Mostly Parallel    Multi
                         Stop-the-world    Mostly concurrent

Concurrent Old only      Serial            CMS
-XX:+UseConcMarkSweepGC  Mostly Parallel   Mostly Parallel    Multi
                         Stop-the-world    Mostly concurrent

Garbage First (G1)       Garbage First     Garbage First      Multi
-XX:+UseG1GC             Mostly Parallel   Mostly Parallel
                         Stop-the-world    Mostly concurrent
						
Z - 1 Generation                     Z                        Multi
-XX:+UseZGC                          Mostly Parallel
                                     Mostly concurrent

Note that:

Next, we will discuss each GC combination individually.

Table of Contents

 About This Book

 Heap Memory Area and Size Control

 JVM Garbage Collection Logging

Introduction of Garbage Collectors

 JVM Memory Manager - Garbage Collector

 Generational Garbage Collection in HotSpot

 Young Generation Collection - Minor GC

 Young Generation Collectors - Serial, PS, ParNew, G1

 Tenured Generation Collection - Major GC

 Tenured Generation Collectors - Serial, ParOldGen, CMS, G1

Collector Combinations: Serial, Parallel, Concurrent, G1, Z

 Serial Collector - "+XX:+UseSerialGC"

 Parallel Collector - "+XX:+UseParallelGC"

 Concurrent Mark-Sweep (CMS) Collector - "+XX:+UseConcMarkSweepGC"

 Garbage First (G1) Collector - "+XX:+UseG1GC"

 The Z Garbage Collector (ZGC) - "+XX:+UseZGC"

 Object References and Garbage Collection

 Garbage Collection Performance Test Program

 Performance Tests on Serial Collector

 Performance Tests on Parallel collector

 Performance Tests on Concurrent collector

 Performance Tests on G1 collector

 Garbage Collection Performance Test Summary

 References

 Full Version in PDF/EPUB