ZGC cores on linux-x64 are noticeably bigger on linux-x64 than with G1, but are still relatively small. SA core file tests that crash on startup will have about a 1gb core with G1 on linux-x64 and 2.5gb on with ZGC. This is with no other heap related settings.

However, on OSX core files sizes are a lot bigger in general than with linux-x64. For example, the same SA core tests produce a 6gb core file with G1 on OSX compared to the 1gb on linux-x64 mentioned above. ZGC greatly magnifies this increase in core file size, and the same SA tests are producing 80gb core files with the OSX + ZGC combination.

Another experiment that was done on core files sizes was to start the JVM with -Xmx128m and then force core dump by using gcore. The G1 core was 3gb and the ZGC core was 18gb.

And one more experiment was done on an MBPro (not a mach5 host). The JVM was launched with -XX:ErrorHandlerTest=1. This created an 8gb core file with G1. With ZGC the core file was 220gb, but the host also crashed due to running out of disk space, so it could actually have been larger than this.