Switching away from the ZST component

Using just the zing-jdk package on recent Zing versions is the recommended way for most use cases.

Since Zing version 19.07 released in the year 2019, the ZST component as package zing-zst, is not needed for most use cases. It is only absolutely needed for heapsizes above 14000 GBytes on current x86_64 server CPUs (14 TBytes)  or when running on old Linux versions like RHEL 6. On arm64 / aarch64 ZST is not available at all and the heapsize limit is already higher at 5600 GBytes.

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
• SHMEM-THP: https://docs.azul.com/prime/Enable-Huge-Pages

Switching away from ZST usually just means to not install the zing-zst package at all and install only the zing-jdk package. If you already have installed ZST, just uninstall the zing-zst package only, 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

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