Why Aikar flags?

Aikar studied the JVM flags for several weeks before ending with these. The G1 garbage collector offers a great stability with decent performance, but may be slow in certain situations. It helped big servers at that time and it still helps them nowadays, but Java evolved. More and more garbage collectors are being created, and a good alternative today would be ShenandoahGC, tho it drastically increases CPU usage. In a near future, ZGC will be the reference of garbage collectors for Minecraft server, but it is still in development and kills your CPU, for real. That's why I stick to the G1GC.

Disclaimer

First and foremost, I cannot be held responsible for any problems on your server as a result of these changes. This is still experimental and bugs can happen. No one has the same configuration, everything can vary from person to person.

Java distribution

GraalVM aims to provide high-performance runtime with new compiler optimizations. It is available for Java 11 & 17. You can grab the Community Edition here, tho a part of the flags won't work without the Enterprise Edition.

Flags

From 1.17, Java 16 is the minimal requirement. If you're using older versions, I recommend using Java 11. Never ever use Java 8, it's a 7 years old version and has bad performance.

Supported server softwares:

• Vanilla
• Spigot/Paper and its multiple forks… (Airplane is recommended)
• Sponge
• Fabric
• Forge

For servers using 12GB of RAM or less:

java -server -Xms8G -Xmx8G -XX:+UseG1GC -XX:+ParallelRefProcEnabled -XX:MaxGCPauseMillis=200 -XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+DisableExplicitGC -XX:+AlwaysPreTouch -XX:G1NewSizePercent=30 -XX:G1MaxNewSizePercent=40 -XX:G1HeapRegionSize=8M -XX:G1ReservePercent=20 -XX:G1HeapWastePercent=5 -XX:G1MixedGCCountTarget=4 -XX:InitiatingHeapOccupancyPercent=15 -XX:G1MixedGCLiveThresholdPercent=90 -XX:G1RSetUpdatingPauseTimePercent=5 -XX:SurvivorRatio=32 -XX:+PerfDisableSharedMem -XX:MaxTenuringThreshold=1 -Dusing.aikars.flags=https://mcflags.emc.gs -Daikars.new.flags=true -XX:-UseBiasedLocking -XX:+EnableJVMCIProduct -XX:+EnableJVMCI -XX:+UseJVMCICompiler -XX:+EagerJVMCI -XX:UseAVX=2 -XX:+UseStringDeduplication -XX:+UseFastUnorderedTimeStamps -XX:+UseAES -XX:+UseAESIntrinsics -XX:UseSSE=4 -XX:AllocatePrefetchStyle=1 -XX:+UseLoopPredicate -XX:+RangeCheckElimination -XX:+EliminateLocks -XX:+DoEscapeAnalysis -XX:+UseCodeCacheFlushing -XX:+UseFastJNIAccessors -XX:+OptimizeStringConcat -XX:+UseCompressedOops -XX:+UseThreadPriorities -XX:+OmitStackTraceInFastThrow -XX:+TrustFinalNonStaticFields -XX:ThreadPriorityPolicy=1 -XX:+UseInlineCaches -XX:+RewriteBytecodes -XX:+RewriteFrequentPairs -XX:+UseNUMA -XX:-DontCompileHugeMethods -XX:+UseCMoveUnconditionally -XX:+UseFPUForSpilling -XX:+UseNewLongLShift -XX:+UseVectorCmov -XX:+UseXMMForArrayCopy -XX:+UseXmmI2D -XX:+UseXmmI2F -XX:+UseXmmLoadAndClearUpper -XX:+UseXmmRegToRegMoveAll -Dfile.encoding=UTF-8 -Djdk.nio.maxCachedBufferSize=262144 -Dgraal.TuneInlinerExploration=1 -Dgraal.CompilerConfiguration=enterprise -Dgraal.UsePriorityInlining=true -Dgraal.Vectorization=true -Dgraal.OptDuplication=true -Dgraal.DetectInvertedLoopsAsCounted=true -Dgraal.LoopInversion=true -Dgraal.VectorizeHashes=true -Dgraal.EnterprisePartialUnroll=true -Dgraal.VectorizeSIMD=true -Dgraal.StripMineNonCountedLoops=true -Dgraal.SpeculativeGuardMovement=true -Dgraal.InfeasiblePathCorrelation=true --add-modules jdk.incubator.vector -jar server.jar nogui

For servers using more than 12GB of RAM:

java -server -Xms16G -Xmx16G -XX:+UseG1GC -XX:+ParallelRefProcEnabled -XX:MaxGCPauseMillis=200 -XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+DisableExplicitGC -XX:+AlwaysPreTouch -XX:G1NewSizePercent=40 -XX:G1MaxNewSizePercent=50 -XX:G1HeapRegionSize=16M -XX:G1ReservePercent=15 -XX:G1HeapWastePercent=5 -XX:G1MixedGCCountTarget=4 -XX:InitiatingHeapOccupancyPercent=20 -XX:G1MixedGCLiveThresholdPercent=90 -XX:G1RSetUpdatingPauseTimePercent=5 -XX:SurvivorRatio=32 -XX:+PerfDisableSharedMem -XX:MaxTenuringThreshold=1 -Dusing.aikars.flags=https://mcflags.emc.gs -Daikars.new.flags=true -XX:-UseBiasedLocking -XX:+EnableJVMCIProduct -XX:+EnableJVMCI -XX:+UseJVMCICompiler -XX:+EagerJVMCI -XX:UseAVX=2 -XX:+UseStringDeduplication -XX:+UseFastUnorderedTimeStamps -XX:+UseAES -XX:+UseAESIntrinsics -XX:UseSSE=4 -XX:AllocatePrefetchStyle=1 -XX:+UseLoopPredicate -XX:+RangeCheckElimination -XX:+EliminateLocks -XX:+DoEscapeAnalysis -XX:+UseCodeCacheFlushing -XX:+UseFastJNIAccessors -XX:+OptimizeStringConcat -XX:+UseCompressedOops -XX:+UseThreadPriorities -XX:+OmitStackTraceInFastThrow -XX:+TrustFinalNonStaticFields -XX:ThreadPriorityPolicy=1 -XX:+UseInlineCaches -XX:+RewriteBytecodes -XX:+RewriteFrequentPairs -XX:+UseNUMA -XX:-DontCompileHugeMethods -XX:+UseCMoveUnconditionally -XX:+UseFPUForSpilling -XX:+UseNewLongLShift -XX:+UseVectorCmov -XX:+UseXMMForArrayCopy -XX:+UseXmmI2D -XX:+UseXmmI2F -XX:+UseXmmLoadAndClearUpper -XX:+UseXmmRegToRegMoveAll -Dfile.encoding=UTF-8 -Djdk.nio.maxCachedBufferSize=262144 -Dgraal.TuneInlinerExploration=1 -Dgraal.CompilerConfiguration=enterprise -Dgraal.UsePriorityInlining=true -Dgraal.Vectorization=true -Dgraal.OptDuplication=true -Dgraal.DetectInvertedLoopsAsCounted=true -Dgraal.LoopInversion=true -Dgraal.VectorizeHashes=true -Dgraal.EnterprisePartialUnroll=true -Dgraal.VectorizeSIMD=true -Dgraal.StripMineNonCountedLoops=true -Dgraal.SpeculativeGuardMovement=true -Dgraal.InfeasiblePathCorrelation=true --add-modules jdk.incubator.vector -jar server.jar nogui

of course, adjust -Xms and -Xmx values to whatever you want

same for your java path and server jar

Sources

GraalVM release notes