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brucethemoose / Minecraft-Performance-Flags-Benchmarks

Sane, Benchmarked Java Flags and Tweaks for Minecraft
MIT License
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java minecraft performance

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This is a guide to tune Java for Minecraft. Every flag and tweak is individually benchmarked to test for regressions, and checked against Java defaults to avoid redundancy.

While these tweaks notably reduce some server and client stutters, expect only modest TPS gains + minimal FPS gains at best, and somewhat increased RAM + CPU usage. And they are no substitute for clearing laggy things out with mods like Spark or Observable.

Discord for questions and such: https://discord.gg/zeFSR9PnUw

Benchmarks

All flags are tested with Benchmark.py script. See the work-in-progress Benchmarks.md.

Picking a Java Runtime

For Minecraft 1.16.5 and up, use Java 17. Some launchers like Curseforge and Prism Launcher ask you to use Java 8 on 1.16.X, but Minecraft 1.16.5+, all 1.18+ mods, and most 1.16.5 mods are compatible with Java 17.

Sometimes Java 11 will work where Java 17 doesn't.

1.12.2 and below generally requires Java 8.

Java runtimes from Azul, Microsoft, Adoptium, Amazon and so on are basically identical. Some notable exceptions:

If you dont know what to pick, I recommend GraalVM EE (see below) or the latest Adoptium Java 17 JRE: https://adoptium.net/

Couleur maintains a good running list of JREs here: https://rentry.co/JREs

Base Java Flags

These optimized flags run with any Java 11+ build. They work on both servers and clients:

-XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+AlwaysActAsServerClassMachine -XX:+AlwaysPreTouch -XX:+DisableExplicitGC -XX:+UseNUMA -XX:NmethodSweepActivity=1 -XX:ReservedCodeCacheSize=400M -XX:NonNMethodCodeHeapSize=12M -XX:ProfiledCodeHeapSize=194M -XX:NonProfiledCodeHeapSize=194M -XX:-DontCompileHugeMethods -XX:MaxNodeLimit=240000 -XX:NodeLimitFudgeFactor=8000 -XX:+UseVectorCmov -XX:+PerfDisableSharedMem -XX:+UseFastUnorderedTimeStamps -XX:+UseCriticalJavaThreadPriority -XX:ThreadPriorityPolicy=1 -XX:AllocatePrefetchStyle=3

You must add garbage collection flags to these java arguments.

A full set of flags looks like this: -Xmx8G -Xms8G -XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+AlwaysPreTouch -XX:+DisableExplicitGC -XX:+UseNUMA -XX:NmethodSweepActivity=1 -XX:ReservedCodeCacheSize=400M -XX:NonNMethodCodeHeapSize=12M -XX:ProfiledCodeHeapSize=194M -XX:NonProfiledCodeHeapSize=194M -XX:-DontCompileHugeMethods -XX:MaxNodeLimit=240000 -XX:NodeLimitFudgeFactor=8000 -XX:+UseVectorCmov -XX:+PerfDisableSharedMem -XX:+UseFastUnorderedTimeStamps -XX:+UseCriticalJavaThreadPriority -XX:ThreadPriorityPolicy=1 -XX:AllocatePrefetchStyle=3 -XX:+UseG1GC -XX:MaxGCPauseMillis=37 -XX:+PerfDisableSharedMem -XX:G1HeapRegionSize=16M -XX:G1NewSizePercent=23 -XX:G1ReservePercent=20 -XX:SurvivorRatio=32 -XX:G1MixedGCCountTarget=3 -XX:G1HeapWastePercent=20 -XX:InitiatingHeapOccupancyPercent=10 -XX:G1RSetUpdatingPauseTimePercent=0 -XX:MaxTenuringThreshold=1 -XX:G1SATBBufferEnqueueingThresholdPercent=30 -XX:G1ConcMarkStepDurationMillis=5.0 -XX:G1ConcRSHotCardLimit=16 -XX:G1ConcRefinementServiceIntervalMillis=150 -XX:GCTimeRatio=99 -XX:+UseLargePages -XX:LargePageSizeInBytes=2m

Memory Allocation

Minimum and maximum (-xms and -xmx) memory should be set to the same value, as explained here: https://dzone.com/articles/benefits-of-setting-initial-and-maximum-memory-siz

One exception: if you are on a low-memory system, and Minecraft takes up almost all your RAM, set your minimum memory below your maximum memory to conserve as much as possible.

Sizes are set in megabytes (-Xms4096M) or gigabytes (-Xmx8G)

Allocating too much memory can break gc or just slow Minecraft down, even if you have plenty to spare. Allocating too little can also slow down or break the game. Keep a close eye on the Windows Task manager (or your DE's system monitor) as Minecraft is running, and allocate only as much as it needs (which is usually less than 8G). sparkc gcmonitor will tell you if your allocation is too high (the pauses will be too long) or too low (frequent GC with a low memory warning in the notification).

Garbage Collection

Garbage collection flags must be added to Minecraft servers and clients, as the default "pauses" to stop and collect garbage manifest as stutters on the client and lag on servers. Use the /sparkc gcmonitor command in the Spark mod to observe pauses in-game. Any old generation pauses are bad, and young generation G1GC collections should be infrequent, but short enough to be imperceptible.

Pick one set of flags. I recommend Shenandoah on clients, ZGC on powerful Java 17 servers, and G1GC on Graal or on servers/clients with less RAM and fewer cores:

ZGC

ZGC is great for high memory/high core count servers. It has no server throughput hit I can measure, and absolutely does not stutter. However, it requires more RAM and more cores than other garbage collectors.

Unfortunately, it has a significant client FPS hit on my (8-core/16 thread) laptop. See the "ZGC" benchmark in the benchmarks folder. Its not available in Java 8, and much less performant in Java 11 than in Java 17.

-XX:+UseZGC -XX:AllocatePrefetchStyle=1 -XX:-ZProactive enables it, but allocate more RAM and more ConcGCThreads than you normally would for other GC. Note that ZGC does not like AllocatePrefetchStyle=3, hence setting it to 1 overrides the previous entry. U

Shenandoah

Shenandoah performs well on clients, but kills server throughput in my tests. Enable it with -XX:+UseShenandoahGC -XX:ShenandoahGCMode=iu -XX:ShenandoahGuaranteedGCInterval=1000000 -XX:AllocatePrefetchStyle=1

See more tuning options here. The "herustic" and "mode" options don't change much for me (except for "compact," which you should not use). Like ZGC, Shenandoah does not like AllocatePrefetchStyle=3.

Note that Shenandoah is not in Java 8. Its also not in any Oracle Java builds! If you are a Java 8 user, you must use Red Hat OpenJDK to use Shenandoah: https://developers.redhat.com/products/openjdk/download

Client G1GC

G1GC is the default garbage collector, and is the only available garbage collector for GraalVM users. Aikar's famous Minecraft server G1GC arguments run great on clients, with two caveats: they effectively clamp the MaxGCPauseMillis parameter by setting G1NewSizePercent so high, producing long stutters on some clients, and they collect oldgen garbage too aggressively (as the client produces far less than a populated server).

These are similar to the aikar flags, but with shorter, more frequent pauses, less aggressive G1 mixed collection and more aggressive background collection: -XX:+UseG1GC -XX:MaxGCPauseMillis=37 -XX:+PerfDisableSharedMem -XX:G1HeapRegionSize=16M -XX:G1NewSizePercent=23 -XX:G1ReservePercent=20 -XX:SurvivorRatio=32 -XX:G1MixedGCCountTarget=3 -XX:G1HeapWastePercent=20 -XX:InitiatingHeapOccupancyPercent=10 -XX:G1RSetUpdatingPauseTimePercent=0 -XX:MaxTenuringThreshold=1 -XX:G1SATBBufferEnqueueingThresholdPercent=30 -XX:G1ConcMarkStepDurationMillis=5.0 -XX:G1ConcRSHotCardLimit=16 -XX:G1ConcRefinementServiceIntervalMillis=150 -XX:GCTimeRatio=99

G1NewSizePercent and MaxGCPauseMillis can be used to tune the frequency/dureation of your young generation collections. G1HeapWastePercent=18 should be removed if you are getting any old generation pauses on your setup. Alternatively, you can raise it and set G1MixedGCCountTarget to 2 or 1 to make mixed garbage collection even lazier (at the cost of higher memory usage).

Server G1GC

Longer pauses are more acceptable on servers. These flags are very close to the aikar defaults:

-XX:+UseG1GC -XX:MaxGCPauseMillis=130 -XX:+UnlockExperimentalVMOptions -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:G1SATBBufferEnqueueingThresholdPercent=30 -XX:G1ConcMarkStepDurationMillis=5 -XX:G1ConcRSHotCardLimit=16 -XX:G1ConcRefinementServiceIntervalMillis=150

Garbage Collection Threading

-XX:ConcGCThreads=[Some Number] controls the maximum number of background threads the garbage collector is allowed to use, and defaults to logical (hyperthreaded) cores / 4. Recent versions of Java will reduce the number of gc threads, if needed.

In some cases (especially with ZGC or Shenandoh) you want to increase this thread cap past the default. I recommend "2" on CPUs with 4 threads, and [number of real cores - 2] on most other CPUs, but you may need to play with this parameter. If its too low, garbage collection can't keep up with Minecraft, and the game will stutter and/or start eating gobs of RAM and crash. If its too high, it might slow the game down, especially if you are running Java 8.

No other "threading" flags like ParallelGCThreads or JVMCIThreads are necessary, as they are enabled by default with good automatic settings in Java 8+.

Large Pages

NOTE: Large Pages requires admin privledges on Windows. This is a security risk, and you should skip this section if you aren't comfortable with that.

Enabling large pages improves the performance of Minecraft servers and clients. Here are some great tutorials for enabling it:

On Windows, you must run java, and your launcher, as an administrator. That means checking the "run as administrator" compatibility checkbox for javaw.exe, java.exe and your launcher.exe, otherwise Large Pages will silently fail. Add -XX:+UseLargePages -XX:LargePageSizeInBytes=2m to your arguments.

On linux, you generally want to use -XX:+UseTransparentHugePages. To manually allocate memory instead (for a bigger performance boost), Red Hat has a good tutorial for RHEL-like linux distros, like Fedora, CentOS, or Oracle Linux: https://www.redhat.com/en/blog/optimizing-rhel-8-run-java-implementation-minecraft-server

Check and see if large pages is working with the -Xlog:gc+init java argument in Java 17.

In any Java version/platform, if large pages isn't working, you will get a warning in the log similar to this:

Java HotSpot(TM) 64-Bit Server VM warning: JVM cannot use large page memory because it does not have enough privilege to lock pages in memory.

GraalVM Enterprise Edition

GraalVM is a new Java VM from Oracle that can improve the performance of (modded and vanilla) Minecraft. While client FPS gains are modest, server-side workloads like chunk generation can get a 20%+ boost!

Only GraalVM Enterprise Edition comes with the full set of optimizations. Download it via direct links from Oracle:

Java 17 - Windows AMD64 (64-bit): https://oca.opensource.oracle.com/gds/GRAALVM_EE_JAVA17_22_3_1/graalvm-ee-java17-windows-amd64-22.3.1.zip - Linux AMD64 (64-bit): https://oca.opensource.oracle.com/gds/GRAALVM_EE_JAVA17_22_3_1/graalvm-ee-java17-linux-amd64-22.3.1.tar.gz - Linux AARCH64 (ARM 64-bit): https://oca.opensource.oracle.com/gds/GRAALVM_EE_JAVA17_22_3_1/graalvm-ee-java17-linux-aarch64-22.3.1.tar.gz - Mac AMD64 (64-bit): https://oca.opensource.oracle.com/gds/GRAALVM_EE_JAVA17_22_3_1/graalvm-ee-java17-darwin-amd64-22.3.1.tar.gz
Java 11 - Windows AMD64 (64-bit): https://oca.opensource.oracle.com/gds/GRAALVM_EE_JAVA11_22_3_1/graalvm-ee-java11-windows-amd64-22.3.1.zip - Linux AMD64 (64-bit): https://oca.opensource.oracle.com/gds/GRAALVM_EE_JAVA11_22_3_1/graalvm-ee-java11-linux-amd64-22.3.1.tar.gz - Linux AARCH64 (ARM 64-bit): https://oca.opensource.oracle.com/gds/GRAALVM_EE_JAVA11_22_3_1/graalvm-ee-java11-linux-aarch64-22.3.1.tar.gz - Mac AMD64 (64-bit): https://oca.opensource.oracle.com/gds/GRAALVM_EE_JAVA11_22_3_1/graalvm-ee-java11-darwin-amd64-22.3.1.tar.gz
Java 8 - Windows AMD64 (64-bit): https://oca.opensource.oracle.com/gds/GRAALVM_EE_JAVA8_21_3_5/graalvm-ee-java8-windows-amd64-21.3.5.zip - Linux AMD64 (64-bit): https://oca.opensource.oracle.com/gds/GRAALVM_EE_JAVA8_21_3_5/graalvm-ee-java8-linux-amd64-21.3.5.tar.gz - Mac AMD64 (64-bit): https://oca.opensource.oracle.com/gds/GRAALVM_EE_JAVA8_21_3_5/graalvm-ee-java8-darwin-amd64-21.3.5.tar.gz

(Select GraalVM EE versions are also available on the AUR and on Oracle Linux's repos)

New versions for ARM Macs require a free registration on Oracle's main download page: https://www.oracle.com/downloads/graalvm-downloads.html

These releases are not Java installers. You need to manually replace your launcher's version of Java, or use a Minecraft launcher that supports specifying your Java path. I recommend ATLauncher, Prism Launcher or GDLauncher. When specifying a java path, navigate to the "bin" folder in the GraalVM download and use "javaw.exe" or "java.exe".

For servers, you need to replace the "java" command in your server start sh/bat file with the full path to graalvm java, in quotes.

Alternatively, you can install it system-wide by following Oracle's guide: https://www.graalvm.org/22.2/docs/getting-started/#install-graalvm

GraalVM EE Java Arguments

Arguments for GraalVM EE 22+ Java 17 (or Java 11):

-XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions -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:-DontCompileHugeMethods -XX:+PerfDisableSharedMem -XX:+UseFastUnorderedTimeStamps -XX:+UseCriticalJavaThreadPriority -XX:+EagerJVMCI -Dgraal.TuneInlinerExploration=1 -Dgraal.CompilerConfiguration=enterprise

You must use G1GC with these arguments. GraalVM currently doesn't work with ZGC or Shenandoah.

GraalVM EE Mod Compatibility

GraalVM EE 22.3.0 fixes all known Minecraft bugs

If you run an older, Java 8-based version of GraalVM, there are some potential issues:

I have not observed any server-side bugs yet.

If you run into any other mod issues you can trace back to GraalVM, please create a Github issue or post in the Discord! Generally, you can work around them by disabling major dgraal optimization flags, or by finding the right function with Dgraal.PrintCompilation=true, and working around it with -Dgraal.GraalCompileOnly=~... once you find the miscompiled function.

SpecialK

A "universal" Windows mod akin to ReShade, SpecialK has 2 major performance benefits:

Download it here: https://wiki.special-k.info/en/SpecialK/Tools

Add your MC launcher, and check the "elevated service" checkbox. Then navigate to your java bin folder where your javaw.exe is, and create an empty file called SpecialK.OpenGL32. Launch your Minecraft launcher with the SpecialK launcher, and the launcher will then "inject" SpecialK into Minecraft. SpecialK

You can create a desktop shortcut to your Minecraft launcher through the SpecialK UI for even more convenience.

Be sure to turn off VSync and the in-game Minecraft frame limiter.

One user has reported reduced FPS when running SpecialK. If this happens to you, please let me know through Discord or Github!

Process Priority

After launching Minecraft, set Java to run at an "Above Normal" process priority in Windows with the Task Manager:

taskmanager

Linux users can add sudo nice -n -10 to the beginning of the launch command, but note that nice levels below 0 (with the "max" being -20) require running Minecraft as sudo. Alternatively, use the renice command after launching Minecraft to avoid this security risk.

Performance Mods

This is a fantastic repo for finding performance mods: https://github.com/NordicGamerFE/usefulmods

Instead of Optifine, I would recommend more compatible alternatives like Sodium + Iris or Rubidium + Oculus.

Java 8

I recommend using Java 17 or, failing that, Java 11 unless 8 is absolutely necessary. But if it is, these flags will work with OpenJDK8, along with Shenandoh GC (for Red Hat OpenJDK on clients) or G1GC (for everything else):

-XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+AlwaysActAsServerClassMachine -XX:+ParallelRefProcEnabled -XX:+DisableExplicitGC -XX:+AlwaysPreTouch -XX:+PerfDisableSharedMem -XX:+AggressiveOpts -XX:+UseFastAccessorMethods -XX:MaxInlineLevel=15 -XX:MaxVectorSize=32 -XX:+UseCompressedOops -XX:ThreadPriorityPolicy=1 -XX:+UseNUMA -XX:+UseDynamicNumberOfGCThreads -XX:NmethodSweepActivity=1 -XX:ReservedCodeCacheSize=350M -XX:-DontCompileHugeMethods -XX:MaxNodeLimit=240000 -XX:NodeLimitFudgeFactor=8000 -XX:+UseFPUForSpilling -Dgraal.CompilerConfiguration=community

x86 Java 8 users (aka most Java 8 users) can add these additional arguments:

-XX:+UseXMMForArrayCopy

You can also get Java 8 versions of GraalVM EE from the 21.X section on the Oracle site, and use these arguments:

-XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+AlwaysActAsServerClassMachine -XX:+ParallelRefProcEnabled -XX:+DisableExplicitGC -XX:+AlwaysPreTouch -XX:+AggressiveOpts -XX:+UseFastAccessorMethods -XX:AllocatePrefetchStyle=1 -XX:ThreadPriorityPolicy=1 -XX:+UseNUMA -XX:+UseDynamicNumberOfGCThreads -XX:NmethodSweepActivity=1 -XX:ReservedCodeCacheSize=350M -XX:-DontCompileHugeMethods -XX:MaxNodeLimit=240000 -XX:NodeLimitFudgeFactor=8000 -XX:+UseFPUForSpilling -XX:+EnableJVMCI -XX:+UseJVMCICompiler -XX:+EagerJVMCI -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

Be sure to set -Dgraal.VectorizeSIMD to false if you run shaders.

Other Performance Tips

FAQ

Flag Explanations

Flags Under Consideration:

Sources