Switching away from the ZST component

The ZST component is deprecated, and support is scheduled to end on September 1, 2027. After this date, Azul will no longer provide updates or support for ZST.

Zing versions released after the year 2019 don't need the ZST component (package zing-zst) anymore, just the zing-jdk or zing-jre package is sufficient on modern operating systems. Zing without ZST on x86_64 supports Java heap sizes up to 14000 GBytes (14 TBytes) or on older hardware 2800 GB (2.8 TBytes). On arm64 / aarch64 the maximum heapsize is currently 5600 GBytes (5.6 TBytes).

When running without ZST in production environments, make sure to apply the following Linux system configurations for best performance, which don't require a reboot:

• vm.max_map_count: https://docs.azul.com/prime/installation-and-configuration#_ensuring-sufficient-virtual-memory-areas
• on x86_64 or arm64 enable SHMEM-THP: https://docs.azul.com/prime/Enable-Huge-Pages
• on arm64 instead of SHMEM-THP you can also use: -XX:+UseTaggedAddressForJavaHeap

Switching away from ZST usually just means to not install the zing-zst package and only install the zing-jdk or zing-jre package. If you already have installed ZST, just uninstall the zing-zst package, which requires all Zing java processes to have stopped and then to be restarted after completing the uninstall. A reboot is not necessary.

On the Zing user side, the following differences are relevant for some use cases:

• default heapsize without -Xmx on the command line on ZST is 1GB while without ZST it is the same as with OpenJDK, 25% of the environment memory but limits itself to 32GB
• without -Xms (initial heapsize) on the command line, it allocates the complete heapsize on start with ZST, while without ZST the allocation will gradually increase like with OpenJDK by demand up to -Xmx (maximum heapsize). Setting -Xms to the value of -Xms will allocate the whole heap on start.
• tools provided with the zing-zst package like zing-licensed and zing-ps won't be available anymore, but for just listing all java processes and checking their vendor names, the alternative jcmd exists
• on older x86_64 CPUs and on many x86_64 cloud based instances the maximum heapsize without ZST is only 2800 GB (2.8 TB). Only on those x86_64 systems where the LA57 CPU feature is available, the heapsize limit without ZST is 14000 GB (14 TB). For example on AWS EC2 only metal type instances offer it. To check if the LA57 feature is available, run this Linux command:
  lscpu | grep -i LA57

If you have questions about switching away from ZST, just ask support@azul.com.