Information

These Java flags are meant for Minecraft servers ran with the GraalVM Java Runtime which you can download from here. They only work on Java 17 and higher and they only run on Linux.

NOTE: These flags were just put together based on a few sources without proper testing on the actual performance impact. Most of these flags aren't GraalVM specific either. For a more sane way of optimizing the Java GC please read this.

GraalVM Java Flags

--add-modules=jdk.incubator.vector -XX:+UseG1GC -XX:MaxGCPauseMillis=130 -XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+DisableExplicitGC -XX:+AlwaysPreTouch -XX:G1NewSizePercent=28 -XX:G1HeapRegionSize=16M -XX:G1ReservePercent=20 -XX:G1MixedGCCountTarget=3 -XX:InitiatingHeapOccupancyPercent=10 -XX:G1MixedGCLiveThresholdPercent=90 -XX:SurvivorRatio=32 -XX:MaxTenuringThreshold=1 -XX:+PerfDisableSharedMem -XX:G1SATBBufferEnqueueingThresholdPercent=30 -XX:G1ConcMarkStepDurationMillis=5 -XX:G1ConcRSHotCardLimit=16 -XX:G1ConcRefinementServiceIntervalMillis=150 -XX:G1RSetUpdatingPauseTimePercent=0 -XX:+UseNUMA -XX:-DontCompileHugeMethods -XX:MaxNodeLimit=240000 -XX:NodeLimitFudgeFactor=8000 -XX:ReservedCodeCacheSize=400M -XX:NonNMethodCodeHeapSize=12M -XX:ProfiledCodeHeapSize=194M -XX:NonProfiledCodeHeapSize=194M -XX:NmethodSweepActivity=1 -XX:+UseFastUnorderedTimeStamps -XX:+UseCriticalJavaThreadPriority -XX:AllocatePrefetchStyle=3 -XX:+AlwaysActAsServerClassMachine -XX:+UseTransparentHugePages -XX:LargePageSizeInBytes=2M -XX:+UseLargePages -XX:+EagerJVMCI -Dgraal.TuneInlinerExploration=1 -Dgraal.LoopRotation=true -Dgraal.OptWriteMotion=true -Dgraal.CompilerConfiguration=enterprise

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Flag Explanations

• --add-modules=jdk.incubator.vector This is only useful for servers running Pufferfish or Purpur on 1.18.2 and above. It enables SIMD operations on your server if they're available and optimizes map rendering.
• -XX:+UseG1GC -XX:MaxGCPauseMillis=130 -XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+DisableExplicitGC -XX:+AlwaysPreTouch -XX:G1NewSizePercent=28 -XX:G1HeapRegionSize=16M -XX:G1ReservePercent=20 -XX:G1MixedGCCountTarget=3 -XX:InitiatingHeapOccupancyPercent=10 -XX:G1MixedGCLiveThresholdPercent=90 -XX:G1RSetUpdatingPauseTimePercent=0 -XX:SurvivorRatio=32 -XX:MaxTenuringThreshold=1 -XX:+PerfDisableSharedMem Generic G1GC flags. These flags are very close to Aikar's.
• -XX:G1SATBBufferEnqueueingThresholdPercent=30 -XX:G1ConcMarkStepDurationMillis=5 -XX:G1ConcRSHotCardLimit=16 -XX:G1ConcRefinementServiceIntervalMillis=150 Optimizes G1GC's concurrent collection threads, the last 2 flags aren't needed in Java 21 anymore.
• -XX:G1RSetUpdatingPauseTimePercent=0 Makes all the work to be done in the G1GC concurrent threads, not the pauses.
• -XX:+UseNUMA Enables optimizations for multisocket systems, if applicable. Not sure if this applies to MCM CPUs like Ryzen or Epyc, but its auto disabled if not applicable.
• -XX:-DontCompileHugeMethods Allows huge methods to be compiled.
• -XX:MaxNodeLimit=240000 -XX:NodeLimitFudgeFactor=8000 Enable optimization of larger methods.
• -XX:ReservedCodeCacheSize=400M -XX:NonNMethodCodeHeapSize=12M -XX:ProfiledCodeHeapSize=194M -XX:NonProfiledCodeHeapSize=194M Reserves more space for compiled code. All sections must "add up" to ReservedCodeCacheSize.
• -XX:NmethodSweepActivity=1 (default 10) Keeps "cold" code in the cache for a longer time. There is no risk of "filling up" the code cache either, as cold code is more aggressively removed as it fills up.
• -XX:+UseFastUnorderedTimeStamps Avoids system calls for getting the time. The impact of this will vary per system, but we aren't really concerned with logging timestamp accuracy.
• -XX:+UseCriticalJavaThreadPriority Nothing should preempt the Minecraft threads. GC and Compiler threads can wait.
• -XX:AllocatePrefetchStyle=3 Generate one prefetch instruction per cache line. More aggressive prefetching is generally useful on newer CPUs with large caches.
• -XX:+UseTransparentHugePages -XX:LargePageSizeInBytes=2M -XX:+UseLargePages Enables Large Pages.
• -XX:+EagerJVMCI Eagers the JVMCI Compiler provided by GraalVM.
• -Dgraal.TuneInlinerExploration=1 -Dgraal.LoopRotation=true -Dgraal.OptWriteMotion=true -Dgraal.CompilerConfiguration=enterprise Generic GraalVM flags.

Sources

• Updated Aikar flags: https://github.com/etil2jz/etil-minecraft-flags
• Red Hat's optimization guide: https://www.redhat.com/en/blog/optimizing-rhel-8-run-java-implementation-minecraft-server
• BruceTheMoose's Java flags benchmarks: https://github.com/brucethemoose/Minecraft-Performance-Flags-Benchmarks