Welcome! this is a guide to tune Java for Minecraft.

Note

1. 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.

2. While these flags are easy to copy-paste and forget, they are no substitute for clearing laggy things out with mods like Spark.

Performance Mods

You might be thinking "This is weird, why are performance mods here?" but performance mods will increase your performance more than any Java flags could, but if you want pure performance, don't just use Optifine. There are better performing mods like Sodium. Sodium also supports Fabric natively (unlike Optifine) and the 0.6 beta supports NeoForge aswell.

For pure performance, you can take a look at Simply Optimized and Adrenaline for examples.

If you want a up-to-date Optifine replacement on the other hand, Fabulously Optimized and Additive both mimic it very well with better performance and customizability.

Picking a Java Distributor

Java runtimes from Azul or Microsoft, Adoptium, Amazon and so on are all basically identical as they are based on OpenJDK. Some notable exceptions are:

1. GraalVM - features a more aggressive Java compiler.

2. Clear Linux OpenJDK - uses a highly compatible OpenJDK base but it's build process and dependencies are optimized for newer CPUs.

3. Platform Prime - very fast since it hooks into llvm, but is currently incompatible with most mods and Linux-only.

4. Red Hat Java 8 - has the Shenandoah garbage collector (It is the only Java 8 JDK with it).

5. OpenJ9 - consumes less memory at the cost of being much slower in Minecraft. It also uses totally different flags than any other Java build.

If you dont know what to pick, I recommend GraalVM or Adoptium. You can download Adoptium from here, and you can download GraalVM from here.

Picking the correct Java version

While any Java Distributor will work just fine, you should choose the correct java version for your game version. You can check the correct version using the Minecraft Wiki. Just search your game version with "Java Edition" at the beginning and check the "Minimum Java Version".

Example:

Memory Allocation

Minimum and maximum memory flags (-xms and -xmx) should be set to the same value as explained here with one caveat: 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. Also try removing these arguments:

-XX:NmethodSweepActivity=1 -XX:ReservedCodeCacheSize=400M -XX:NonNMethodCodeHeapSize=12M -XX:ProfiledCodeHeapSize=194M -XX:NonProfiledCodeHeapSize=194M

and try server garbage collection arguments.

Sizes are set in megabytes or gigabytes so -Xms4096M or -Xmx8G are both correct.

Note

1. Allocating too much memory can break garbage collection 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 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).

2. If you are using a third-party Minecraft launcher like Prism Launcher or ATLauncher, you shouldn't use memory arguments and instead control memory through the dedicated section in the launcher.

Base Java Flags

These are the majority of the flags. The flags below will work for any OpenJDK 11+ build. They are the same on both servers and clients:

-XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+AlwaysActAsServerClassMachine -XX:+AlwaysPreTouch -XX:+DisableExplicitGC -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

For GraalVM Java 17+, use the flags below instead:

-XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+AlwaysActAsServerClassMachine -XX:+AlwaysPreTouch -XX:+DisableExplicitGC -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

For Platform Prime, usually no tuning with special flags is necessary, Large Pages are still applicable though.

And for OpenJ9, you may try the flags below instead, though it isn't recommended to use OpenJ9:

-XX:+IdleTuningGcOnIdle -XX:+UseAggressiveHeapShrink -XX:-OmitStackTraceInFastThrow -XX:+UseFastAccessorMethods -XX:+OptimizeStringConcat -Xshareclasses:allowClasspaths -Xshareclasses:cacheDir=./cache -Xaot -XX:+UseCompressedOops -XX:ObjectAlignmentInBytes=256 -Xshareclasses -XX:SharedCacheHardLimit=800M -Xtune:virtualized -XX:+TieredCompilation -XX:InitialTenuringThreshold=5 -Dlog4j2.formatMsgNoLookups=true -XX:-DisableExplicitGC -XX:InitiatingHeapOccupancyPercent=35 -XX:+UnlockExperimentalVMOptions -XX:MaxGCPauseMillis=6 -Djava.net.preferIPv4Stack=true -XX:-ParallelRefProcEnabled-XX:+UseTLAB -XX:ReservedCodeCacheSize=70M -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20

Java 8

I hightly recommend not using Java 8 unless it is neccesary, but if it is, these flags will work with OpenJDK 8:

-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:+UseDynamicNumberOfGCThreads -XX:NmethodSweepActivity=1 -XX:ReservedCodeCacheSize=350M -XX:-DontCompileHugeMethods -XX:MaxNodeLimit=240000 -XX:NodeLimitFudgeFactor=8000 -XX:+UseFPUForSpilling

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

-XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions -XX:+AlwaysActAsServerClassMachine -XX:+ParallelRefProcEnabled -XX:+DisableExplicitGC -XX:+AlwaysPreTouch -XX:+AggressiveOpts -XX:+UseFastAccessorMethods -XX:ThreadPriorityPolicy=1 -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

Though make sure to set -Dgraal.VectorizeSIMD to false if you run shaders as this version causes issues with them. This old version also breaks constellation rendering in 1.16.5 Astral Sorcery. This is possibly related to the shader bug. See: HellFirePvP/AstralSorcery#1963

Garbage Collection

Garbage collection flags should 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 Spark 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.

Non-Proactive ZGC

Non-Proactive 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. Enable it with

-XX:+UseZGC -XX:AllocatePrefetchStyle=1 -XX:-ZProactive

Note

1. It has a significant client FPS hit.

2. Non-Proactive ZGC is unavailable in Java 8 and much less performant in Java 11 than it is in Java 17+.

3. Allocate more RAM and more ConcGCThreads than you normally would for other GC.

4. GraalVM currently disables EnableJVMCI when using ZGC since it doesn't support it.

Generational ZGC

Generational ZGC is great for high memory/high core count servers and is made to be competitive with the only other Generation GC, G1GC. Enable it with

-XX:+UseZGC -XX:AllocatePrefetchStyle=1 -XX:+ZGenerational

Note

1. Generational ZGC is only available in Java 21+

2. Allocate more RAM and more ConcGCThreads than you normally would for other GC.

3. GraalVM currently disables EnableJVMCI when using ZGC since it doesn't support it.

4. Java 23+ no longer requires -XX:+ZGenerational flag. Remove it if you want as it will just be ignored since Generational is the new default.

Shenandoah

Shenandoah performs well on clients, but kills server throughput. 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 (except for "compact," which you should not use).

Note

1. Red Hat OpenJDK 8 is the only Java 8 JDK that supports Shenandoah.

2. GraalVM currently doesn't support Shenandoah.

Client G1GC

G1GC is the default garbage collector for all JREs. 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:GCTimeRatio=99 -XX:G1ConcRefinementServiceIntervalMillis=150 -XX:G1ConcRSHotCardLimit=16 -XX:AllocatePrefetchStyle=3

Note

1. Java 21+ no longer supports -XX:G1ConcRefinementServiceIntervalMillis=150 flag and the -XX:G1ConcRSHotCardLimit=16 flag. Remove them if you want as they will just be ignored.

2. 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).

3. If you are using a Java 8 based GraalVM EE, change -XX:AllocatePrefetchStyle=3 to -XX:AllocatePrefetchStyle=1

Server G1GC

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

-XX:+UseG1GC -XX:MaxGCPauseMillis=130 -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=5.0 -XX:G1ConcRefinementServiceIntervalMillis=150 -XX:G1ConcRSHotCardLimit=16 -XX:AllocatePrefetchStyle=3

Note

1. Java 21+ no longer supports -XX:G1ConcRefinementServiceIntervalMillis=150 flag and the -XX:G1ConcRSHotCardLimit=16 flag. Remove them if you want as they will just be ignored.

2. 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).

3. If you are using a Java 8 based GraalVM EE, change -XX:AllocatePrefetchStyle=3 to -XX:AllocatePrefetchStyle=1

Garbage Collection Threading

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

In some cases (especially with ZGC or Shenandoah) you want to increase this thread cap past the default. I recommend [number of REAL (non-hyperthreaded) cores - 2] on most 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. Probably keep it under 8 (you can maybe get away with 10 for ZGC and Shenandoah).

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

Caution

Some guides say that you must run Java and your launcher as administrator on Windows. This has been shown wrong and is a MAJOR SECURITY RISK.

Enabling large pages improves the performance of Minecraft servers and clients by reducing the load on your system. Here's a good guide

Note

1. Windows Home doesn't have gpedit.msc and thus, can't follow the guide above, intead use this guide, also since microsoft took down the tool in mention, you have to download it from here.

2. On Linux, you generally want to use -XX:+UseTransparentHugePages.

Add -XX:+UseLargePages -XX:LargePageSizeInBytes=2m to your arguments.

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.

SpecialK

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

• A "smart" frame limiter that reduces stutter, eliminates tearing, saves power, and saves CPU TDP to boost when needed. It even works in conjuction with VRR or Nvidia Reflex.

• A OpenGL-to-DirectX11 wrapper called OpenGL-IK that eliminates Minecraft's windowed mode overhead, and enables other features (like auto-HDR or a resizable borderless window).

Download it here.

Add your Minecraft launcher. 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.

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.

Process Priority

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

Linux users can add sudo nice -n -10 to the beginning of the launch command.

Caution

On Linux, nice levels below 0 (with the "max" being -20) require running nice as root which in turn runs Minecraft as root. This is a security risk. Here are some Workarounds:

1. Start game and run renice -10 -p $(PID) as root instead with the pid of the minecraft instance. This is safe as Minecraft itself is not running as root.

2. Modify /etc/security/limits.conf to allow non-root users to go to negatives. Then just use the normal nice command without sudo. Don't do this one if you don't know what you are doing.

3. "Hacky" way to script it: sudo nice -n -10 su <username> -c. The easiest way but the first 2 are probably better.

Other Performance Tips

• Run Minecraft on Linux! In pretty much every scenario it runs very good, for servers, Clear Linux and RHEL are very well optimized, and for clients, CachyOS/Arch is amazing.

• Make sure the Minecraft client is using your discrete GPU! Check the F3 tab, and force Minecraft to use it in the "Windows Graphics Settings", not the AMD/Nvidia control panel (as they don't seem to work anymore).

• Linux wayland users should research running Minecraft natively on wayland instead of through xwayland.

• Close everything in the background, including Discord, game launchers and your browser! Minecraft is resource intensive, and does not like other apps generating CPU interrupts or eating disk I/O, RAM and so on.