JVM Arguments
Overview
JVM arguments were once crucial for performance optimization in Minecraft when running on older Java versions (such as Java 8).
With modern JVMs (Java 17+), most of these optimizations are no longer necessary, as performance tuning is handled well out of the box.
That said, a few arguments can still provide noticeable improvements.
Keep in mind that JVM tuning is hardware-dependent: an argument that helps on one system may not yield the same results on another.
About Distributions
GraalVM is being discontinued in favor of OpenJDK. We recommend to use Zulu or Temurin.
Useful Arguments
Note
Make sure -Xms and -Xmx have the same size. This makes sure the JVM does not have to resize, and will avoid OOM crashes (if you're using a launcher, make sure Max ram is equal to Min ram)
-XX:+UseCompactObjectHeaders
Reduces the size of object headers in the JVM from 96–128 bits down to 64 bits, lowering heap usage and potentially improving performance. Java 25 made this a product feature (See JEP 450) (See JEP 519)-XX:+UseZGC
Enables the Z Garbage Collector (ZGC), which provides very low latency garbage collection and can virtually eliminate GC pauses.
Notes
- The latest tested Java version for Cleanroom Loader is Java 25, it is recommended to use this version, and to always stick to LTS versions.
- On older CPUs, ZGC can be demanding: it increases RAM usage (since ZGC does not use compressed object pointers) and may reduce performance.
Test your game both with and without ZGC, and compare results. You can revert to Java 25’s default collector (G1GC) by removing-XX:+UseZGC - The use of
-XX:+ZGenerationalis not required when using ZGC. (It is enabled by default in Java 25) - Big heaps can only be correctly handled by ZGC. If using G1GC, make sure to pick reasonable heap sizes (Shouldn't exceed 11-12GB ram)
Thermonuclear_Minecraft_Engineer