Usage Instructions for Azul Zing Builds of OpenJDK

Table of Contents

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These are some recommendations and extra info related to the CRaC support in Azul Zing Builds of OpenJDK (Azul Zing).

Supported CRaC Engine

Only the Warp Engine is available in Azul Zing, check CRaC Engines for more info.

Increase the VMA limit on the host system, especially for the restore:

 sudo sysctl vm.max_map_count=10000000

Enable GC logging and detailed restore tracing to be able to diagnose failures and performance issues. Add the following to the command-line during checkpoint:
```
 -Xlog:gc*=info:file=<path-to-gc-log> -Xlog:crac=debug:crac.log
```
Add the parameter -XX:+CRaCPrintResourcesOnCheckpoint to diagnose checkpoint failures due to open files.
Turn off elastic heaps (unless it is absolutely necessary) by setting Xms (InitialHeapSize) equal to Xmx (MaxHeapSize).
You can improve the startup time during restore by up to 50% with -XX:CRaCEngineOptions=min_zero_gap=2m. However, this option will likely result in an increased size of the image file. See Warp Engine Options for more info.