awesome-kubernetes/docs/jvm-parameters-matrix-table.md

| **JVM Parameters** | **Enable?** | **References / Details** |
|:-------------------|:---|:---|
|-XX:+UseG1GC | Enabled by default in Java 8u191+ | Most important defaults specific to G1 and their default values.<br/> [https://dzone.com/articles/choosing-the-right-gc](https://dzone.com/articles/choosing-the-right-gc)<br/> [https://wiki.openjdk.java.net/display/HotSpot/G1GC+Feedback](https://wiki.openjdk.java.net/display/HotSpot/G1GC+Feedback)<br/> Alternative: Shenandoah GC |
|-XX:+UseShenandoahGC | Alternative to G1GC. | Shenandoah Garbage Collector: experimental in Java 8, newer than G1GC, available in some OpenJDK 8 and newer releases.<br/> [https://wiki.openjdk.java.net/display/shenandoah/Main](https://wiki.openjdk.java.net/display/shenandoah/Main) <br/> [https://dzone.com/articles/7-jvm-arguments-of-highly-effective-applications-1](https://dzone.com/articles/7-jvm-arguments-of-highly-effective-applications-1) |
|-XX:+UseZGC | Yes (JDK 11+) | Z GC : Better Garbage Collector Algorithm than G1 or Shenandoah. JDK 11+ required.<br/> The Z Garbage Collector, also known as ZGC, is a scalable low latency garbage collector designed to meet the following goals:<br/> · Pause times do not exceed 10ms (*)<br/> · Pause times do not increase with the heap or live-set size<br/> · Handle heaps ranging from a 8MB to 16TB in size<br/> At a glance, ZGC is:<br/> · Concurrent<br/> · Region-based<br/> · Compacting<br/> · NUMA-aware<br/> · Using colored pointers<br/> · Using load barriers<br/> At its core, ZGC is a concurrent garbage collector, meaning all heavy lifting work is done while Java threads continue to execute. This greatly limits the impact garbage collection will have on your application's response time.<br/> 7 JVM Arguments of Highly Effective Applications<br/> [https://wiki.openjdk.java.net/display/zgc/Main](https://wiki.openjdk.java.net/display/zgc/Main) |
|-XX:MaxRAMPercentage | Yes | Java 8u191+ required.<br/>The old (and somewhat broken) flags -XX:{Min\|Max}RAMFraction are now deprecated. <br/>There is a new flag -XX:MaxRAMPercentage, that takes a value between 0.0 and 100.0 and defaults to 25.0. <br/>So if there is a 1 GB memory limit, the JVM heap is limited to ~250 MB by default. <br/>While this can certainly be improved — depending on the RAM size and workload — it’s a pretty good default compared to the old behaviour.<br/> [https://medium.com/adorsys/usecontainersupport-to-the-rescue-e77d6cfea712](https://medium.com/adorsys/usecontainersupport-to-the-rescue-e77d6cfea712) |
|-XX:+UseContainerSupport | Enabled by default | Java 8u191+ required (enabled by default in Linux)<br/> [https://medium.com/adorsys/jvm-memory-settings-in-a-container-environment-64b0840e1d9e](https://medium.com/adorsys/jvm-memory-settings-in-a-container-environment-64b0840e1d9e)<br/> [https://medium.com/adorsys/usecontainersupport-to-the-rescue-e77d6cfea712](https://medium.com/adorsys/usecontainersupport-to-the-rescue-e77d6cfea712)<br/> Please note that setting -Xmx and -Xms disables the automatic heap sizing.<br/> # check if +UseContainerSupport is enabled<br/> $ java -XX:+PrintFlagsFinal -version | grep UseContainerSupport<br/> bool UseContainerSupport = true {product}<br/> [https://merikan.com/2019/04/jvm-in-a-container/](https://merikan.com/2019/04/jvm-in-a-container/)<br/> Java 10 introduced +UseContainerSupport (enabled by default) which makes the JVM use sane defaults in a container environment. <br/>This feature is backported to Java 8 since 8u191, potentially allowing a huge percentage of Java deployments in the wild to properly configure their memory. |
|-XshowSettings:vm | Yes | This is a priceless feature to display all the settings of the JVM, together with -XX:+PrintCommandLineFlags it can show a world of hidden stuff.<br/> [http://www.javamonamour.org/2018/11/java-showsettings.html](http://www.javamonamour.org/2018/11/java-showsettings.html) |
|-XX:MaxRAMFraction | No (deprecated) | Requires JDK 8u131+<br/> -XX:MaxRAMFraction deprecated since Java 8u191+ (use -XX:MaxRAMPercentage instead)<br/> [https://dzone.com/articles/running-a-jvm-in-a-container-without-getting-kille](https://dzone.com/articles/running-a-jvm-in-a-container-without-getting-kille)<br/> [https://developers.redhat.com/blog/2017/03/14/java-inside-docker/](https://developers.redhat.com/blog/2017/03/14/java-inside-docker/)<br/> [https://merikan.com/2019/04/jvm-in-a-container/](https://merikan.com/2019/04/jvm-in-a-container/) |
|-XX:+UseCGroupMemoryLimitForHeap | No (deprecated) | JDK 8u131+ required<br/> Deprecated in Java10 & Java8u191+<br/> [https://dzone.com/articles/running-a-jvm-in-a-container-without-getting-kille](https://dzone.com/articles/running-a-jvm-in-a-container-without-getting-kille)<br/> [https://developers.redhat.com/blog/2017/03/14/java-inside-docker/](https://developers.redhat.com/blog/2017/03/14/java-inside-docker/)<br/> [https://merikan.com/2019/04/jvm-in-a-container/](https://merikan.com/2019/04/jvm-in-a-container/)<br/> Java memory management and configuration is still complex. Although the JVM can read cgroup memory limits and adapt memory usage accordingly since Java 9/8u131, <br/>it’s not a golden bullet. You need to know what -XX:+UseCGroupMemoryLimitForHeap does and you need to fine tune some parameters for every deployment. <br/>Otherwise you risk wasting resources and money or getting your containers killed at the worst time possible. -XX:MaxRAMFraction=1 is especially dangerous. <br/>Java 10+ brings a lot of improvements but still needs manual configuration. To be safe, load test your stuff. |
|-XX:+UseStringDeduplication | Yes | [https://www.baeldung.com/jvm-garbage-collectors](https://www.baeldung.com/jvm-garbage-collectors) |
|-XX:+HeapDumpOnOutOfMemoryError<br/> -XX:HeapDumpPath | Yes | When running a JVM in a docker container it is probably wise to use the HeapDumpOnOutOfMemoryError option so if you ever run out of memmory the jvm will write a dump of the heap to disk.<br/> [https://merikan.com/2019/04/jvm-in-a-container/](https://merikan.com/2019/04/jvm-in-a-container/)<br/> [https://dzone.com/articles/7-jvm-arguments-of-highly-effective-applications-1](https://dzone.com/articles/7-jvm-arguments-of-highly-effective-applications-1) |
|-Xss | Test | Increase the thread’s stack size limit by passing the -Xss argument.<br/> [https://dzone.com/articles/7-jvm-arguments-of-highly-effective-applications-1](https://dzone.com/articles/7-jvm-arguments-of-highly-effective-applications-1)<br/> Each application will have tens, hundreds, thousands of threads. Each thread will have its own stack. Each one of them consumes memory. <br/>If their consumption goes beyond a certain limit, then a StackOverflowError is thrown. More details about StackOverflowError and solutions to resolve it can be found in this article.<br/> Linux 64-bit JVM Default thread stack size = 1024k<br/> -Xss2m : This will set the thread's stack size to 2mb |
|-Dsun.net.client.defaultConnectTimeout<br/>-Dsun.net.client.defaultReadTimeout | Yes | [https://dzone.com/articles/7-jvm-arguments-of-highly-effective-applications-1](https://dzone.com/articles/7-jvm-arguments-of-highly-effective-applications-1) |
|-Duser.timeZone | Yes | [https://dzone.com/articles/7-jvm-arguments-of-highly-effective-applications-1](https://dzone.com/articles/7-jvm-arguments-of-highly-effective-applications-1) |
|Enable GC Logging | Check | JDK 8: -XX:+PrintGCDetails -XX:+PrintGCDateStamps -Xloggc:{file-path}<br/> JDK9+: -Xlog:gc*:file={file-path}<br/> [https://dzone.com/articles/7-jvm-arguments-of-highly-effective-applications-1](https://dzone.com/articles/7-jvm-arguments-of-highly-effective-applications-1) |
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