Cooperly / v2flags

Absolutely ridiculous JVM flags to dial Minecraft server performance to stupid levels. (Best paired with GraalVM)

Why not just use Aikar's flags?

His GC is based on G1, it's extremely stable but extremely slow, so why should current gen servers be held back by last gen algorithms?

I propose to get rid of it in favor of ZGC, why? It clears memory alongside the server instead of pausing it each time, and it's pretty fast.

Who should use these flags?

Generally modded servers or large networks will probably benefit the most from performance flags.

Smaller servers or clients with limited resources could also see major uplifts with stability flags.

When using these flags you should try to use GraalVM as your java runtime if possible

Some versions have ZGC support and some don't, do research, do testing. If you can't get it working with performance flags then just run it with your pre existing java runtime or see if stability flags provide more performance with GraalVM than your current runtime with performance flags.

Heads Up

Do not rely on these flags as your only source of optimization, yes they could theoretically increase your performance up to 50%, but to be brutally honest it's snake oil compared to optimizing your server properly, use this as a cherry on top in terms of performance, not your entire optimization

I will have an advanced guide out soon for players who want the absolute best performance with no regard to stability, which is probably not a really good idea but I mean if your absolutely crazy like I am, just go for gold you got nothing to lose. in the meantime use this guide.

Flags

• Vanilla (Not recommended, use Leaf, Mirai or Paper.)
• Leaf / Mirai / Paper
• Folia
• Fabric
• Quilt
• Forge
• NeoForge
• Most JVM server software, even non-minecraft (No guarantee, not recommended.)

Performance Focused / Server / More than 12GB, ZGC:

Use these flags only on a server that needs performance that has more than 12GB available.

(Not suggested for clients unless you have an extremely high class machine)

java -Xms12G -Xmx12G -XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+UseZGC -XX:-ZUncommit -XX:-ZProactive -Dterminal.jline=false -Dterminal.ansi=true -Djline.terminal=jline.UnsupportedTerminal -Dlog4j2.formatMsgNoLookups=true -XX:+AlwaysActAsServerClassMachine -XX:+AlwaysPreTouch -XX:+DisableExplicitGC -XX:+UseNUMA -XX:NmethodSweepActivity=1 -XX:ReservedCodeCacheSize=400M -XX:NonNMethodCodeHeapSize=12M -XX:ProfiledCodeHeapSize=194M -XX:NonProfiledCodeHeapSize=194M -XX:+PerfDisableSharedMem -XX:+UseFastUnorderedTimeStamps -XX:+UseCriticalJavaThreadPriority -XX:+EagerJVMCI -Dgraal.TuneInlinerExploration=1 -Dgraal.CompilerConfiguration=enterprise -XX:+ParallelRefProcEnabled -XX:InitiatingHeapOccupancyPercent=15 -XX:SurvivorRatio=32 -XX:MaxTenuringThreshold=1 -XX:-UseBiasedLocking -XX:+UseStringDeduplication -XX:+UseAES -XX:+UseAESIntrinsics -XX:+UseFMA -XX:+UseLoopPredicate -XX:+RangeCheckElimination -XX:+EliminateLocks -XX:+DoEscapeAnalysis -XX:+UseCodeCacheFlushing -XX:+SegmentedCodeCache -XX:+UseFastJNIAccessors -XX:+OptimizeStringConcat -XX:+UseCompressedOops -XX:+UseThreadPriorities -XX:+OmitStackTraceInFastThrow -XX:+TrustFinalNonStaticFields -XX:ThreadPriorityPolicy=1 -XX:+UseInlineCaches -XX:+RewriteBytecodes -XX:+RewriteFrequentPairs -XX:-DontCompileHugeMethods -XX:+UseFPUForSpilling -XX:AllocatePrefetchStyle=1 -XX:+UseVectorCmov -XX:+UseXMMForArrayCopy -XX:+UseLargePages -XX:LargePageSizeInBytes=2M -Dfile.encoding=UTF-8 -Xlog:async -Djava.security.egd=file:/dev/urandom --add-modules jdk.incubator.vector -jar server.jar –-nogui

Stability Focused / Client, Server / Less than 12GB, G1GC:

Use these flags on a server that prefers stability over performance, or has less than 12GB available

(Clients can work however not tested properly)

java -Xms8G -Xmx8G -XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=30 -XX:G1MaxNewSizePercent=40 -XX:G1HeapRegionSize=8M -XX:G1ReservePercent=20 -XX:G1HeapWastePercent=5 -XX:G1MixedGCCountTarget=4 -XX:G1MixedGCLiveThresholdPercent=90 -XX:G1RSetUpdatingPauseTimePercent=5 -Dterminal.jline=false -Dterminal.ansi=true -Djline.terminal=jline.UnsupportedTerminal -Dlog4j2.formatMsgNoLookups=true -XX:+AlwaysActAsServerClassMachine -XX:+AlwaysPreTouch -XX:+DisableExplicitGC -XX:+UseNUMA -XX:AllocatePrefetchStyle=3 -XX:NmethodSweepActivity=1 -XX:ReservedCodeCacheSize=400M -XX:NonNMethodCodeHeapSize=12M -XX:ProfiledCodeHeapSize=194M -XX:NonProfiledCodeHeapSize=194M -XX:+PerfDisableSharedMem -XX:+UseFastUnorderedTimeStamps -XX:+UseCriticalJavaThreadPriority -XX:+EagerJVMCI -Dgraal.TuneInlinerExploration=1 -Dgraal.CompilerConfiguration=enterprise -XX:+ParallelRefProcEnabled -XX:MaxGCPauseMillis=200 -XX:InitiatingHeapOccupancyPercent=15 -XX:SurvivorRatio=32 -XX:MaxTenuringThreshold=1 -XX:-UseBiasedLocking -XX:+UseStringDeduplication -XX:+UseAES -XX:+UseAESIntrinsics -XX:+UseFMA -XX:+UseLoopPredicate -XX:+RangeCheckElimination -XX:+EliminateLocks -XX:+DoEscapeAnalysis -XX:+UseCodeCacheFlushing -XX:+SegmentedCodeCache -XX:+UseFastJNIAccessors -XX:+OptimizeStringConcat -XX:+UseCompressedOops -XX:+UseThreadPriorities -XX:+OmitStackTraceInFastThrow -XX:+TrustFinalNonStaticFields -XX:ThreadPriorityPolicy=1 -XX:+UseInlineCaches -XX:+RewriteBytecodes -XX:+RewriteFrequentPairs -XX:-DontCompileHugeMethods -XX:+UseFPUForSpilling -XX:+UseVectorCmov -XX:+UseXMMForArrayCopy -XX:+UseLargePages -XX:LargePageSizeInBytes=2M -Dfile.encoding=UTF-8 -Xlog:async -Djava.security.egd=file:/dev/urandom --add-modules jdk.incubator.vector -jar server.jar –-nogui

Warning Option UseBiasedLocking was deprecated in version 15.0 and will likely be removed in a future release. can be completely ignored without consequences, it won't effect anything and is unlikely to be removed anytime soon.

Don't forget to adjust -Xms and -Xmx to your server configuration, along with java path and server.jar if applicable

Do not allocate more than 32GB on stability flags, G1GC will start to struggle. Performance flags may go as high as they need but not lower than 12GB. Using more than 20GB is generally over-overkill 99.99% of the time unless your in a heavily modded environment

(according to documentation, untested)

Explanation

Please try not to rely on these explanations, do your own research as I don't know how to explain things due to my anxiety
Kudos to Nova for filling some things here with more understandable information

Note

For most of the flags below -XX:+UnlockExperimentalVMOptions and/or -XX:+UnlockDiagnosticVMOptions are required.

-Xmx8G

Specifies the maximum amount of memory the JVM may use in gigabytes

-Xms8G

Specifies the initial heap size for the JVM in gigabytes

Note

Setting both -Xms and Xmx to the same size is recommended to improve predictability, and to have less GC cycles.

-XX:+UseZGC

Tells the JVM to use the ZGC garbage collector

-XX:-ZUncommit

Stops ZGC from returning memory back to the OS. This can help improve speed as it doesn't have to wait for the OS to reallocate the memory but may also result on undesirably high memory usage and may negatively impact environments where multiple applications are running

-XX:MaxGCPauseMillis=200

Tells JVM to try and keep it's GC (Garbage collector) pauses to or under this specified amount of time. However this only a target and not a guarantee. Doesn't work with -XX:+UseZGC

-XX:+UseG1GC -XX:G1NewSizePercent=30 -XX:G1MaxNewSizePercent=40 -XX:G1HeapRegionSize=8M -XX:G1ReservePercent=20 -XX:G1HeapWastePercent=5 -XX:G1MixedGCCountTarget=4 -XX:G1MixedGCLiveThresholdPercent=90 -XX:G1RSetUpdatingPauseTimePercent=5 -XX:MaxGCPauseMillis=200

Tells java while using stability flags to use G1GC and make short pauses instead of long ones.

-XX:+AlwaysActAsServerClassMachine

Forces java to use garbage collection that would be used with "Server class" hardware. Should show benefits on systems with higher core count CPUs as garbage can be passed of to another thread. ParallelGC, CMS (Concurrent Mark Sweep) or G1GC will be used instead of SerialGC

-XX:+AlwaysPreTouch

Pre-touches memory during allocation, causing them to be loaded into physical memory. Can reduce delays accessing newly allocated memory.

-XX:+DisableExplicitGC

Prevents forced GC calls (By a plugin, or other code), only allowing one's by the JVM itself

-XX:+UseNUMA

Tells JVM that the system uses Non-uniform Memory Access (NUMA), increasing the use of lower latency memory on multi-node topologies (Caches or RAM). Only available when used with -XX:+UseParallelGC

-XX:AllocatePrefetchStyle=3

Enables pre-fetching and set's the prefetch style
0 - Disables any pre-fetching
1 (Default) - Prefetches object fields (Increasing access speed as the fields likely are already loaded into cache)
2 - Prefetches data right before allocation (Thus reducing latency for access to non-cached data)
3 - Prefetches data after allocation (Potentially making access to a objects fields faster)
Setting to "3" has been recommend for use with Minecraft as it improves performance

-XX:+PerfDisableSharedMem

Disables a section of shared memory (A memory mapped file) used for performance statistics. This is done synchronously and can cause performance impacts

XX:+ParallelRefProcEnabled

Allows for parallel reference processing whenever possible.

-XX:-UseBiasedLocking

Improves performance of un-contended synchronization, also spits an error on startup about depreciation which you should ignore

-XX:+UseStringDeduplication

Saves some memory by referencing similar string objects instead of keeping duplicates.

XX:+UseAES -XX:+UseAESIntrinsics -XX:+UseFMA

Enables AES/FMA which very slightly improves performance however is incompatible on >2009 CPUS. Unintentionally also fixes a Geyser bug

-XX:+UseCodeCacheFlushing

Removes old methods from cache

-XX:+UseThreadPriorities

Allows a JVM app like minecraft or mods/plugins to set priority of a thread, good for Folia, C2ME or DimThread

-jar server.jar

Tells java what the name of the jar executable is

–-nogui

Forces games like minecraft to not display the funky gui, does not matter in non graphical enviroments, I personally remove this flag when running JVM servers on my machine.

-Dterminal.jline=false -Dterminal.ansi=true -Djline.terminal=jline.UnsupportedTerminal Dlog4j2.formatMsgNoLookups=true -XX:NmethodSweepActivity=1 -XX:ReservedCodeCacheSize=400M -XX:NonNMethodCodeHeapSize=12M -XX:ProfiledCodeHeapSize=194M -XX:NonProfiledCodeHeapSize=194M -XX:+UseFastUnorderedTimeStamps -XX:+UseCriticalJavaThreadPriority -XX:+EagerJVMCI -Dgraal.TuneInlinerExploration=1 -Dgraal.CompilerConfiguration=enterprise -XX:InitiatingHeapOccupancyPercent=15 -XX:SurvivorRatio=32 -XX:MaxTenuringThreshold=1 -XX:+UseLoopPredicate -XX:+RangeCheckElimination -XX:+EliminateLocks -XX:+DoEscapeAnalysis -XX:+SegmentedCodeCache -XX:+UseFastJNIAccessors -XX:+OptimizeStringConcat -XX:+UseCompressedOops -XX:+OmitStackTraceInFastThrow XX:+TrustFinalNonStaticFields -XX:+UseInlineCaches -XX:+RewriteBytecodes -XX:+RewriteFrequentPairs -XX:-DontCompileHugeMethods -XX:+UseFPUForSpilling -XX:+UseVectorCmov -XX:+UseXMMForArrayCopy Dfile.encoding=UTF-8 -Xlog:async -Djava.security.egd=file:/dev/urandom --add-modules jdk.incubator.vector -XX:+UseLargePages -XX:LargePageSizeInBytes=2M -XX:ThreadPriorityPolicy=1

These flags are generally either GraalVM specific optimizations which optimize performance, or they make such little difference in how a JVM app works that they don't deserve documentation on this page for the sake of my own sanity, do your own research.

Note

Not all values and flags may have been explained properly, as information was extremely hard to come by and especially in an explainable format, You may get more correct information from other sources.

Notice

These flags aren't as rigorously tested as something like Aikar's Flags, although the chances are extremely slim, you could encounter problems like crashing or in the absolute worst case scenario, even corruption.

USE THEM AT YOUR OWN RISK! v2k or anybody affiliated is not responsible for any damages as a result of these flags being used, You are on your own and no support will be given.