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.

Useful Arguments

• -XX:+UnlockExperimentalVMOptions -XX:+UseCompactObjectHeaders
  Introduced in Java 24.
  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
  
• 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 24’s default collector (G1GC) by removing -XX:+UseZGC
  
• The use of -XX:+ZGenerational is not required when using ZGC. (It is enabled by default in Java 25)
  

Contributors

Thermonuclear_Minecraft_Engineer

Last edited 23 days ago

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