Aikar's JVM Flags for Minecraft Servers Explained

Aikar's flags are a set of JVM (Java Virtual Machine) arguments that optimize garbage collection for Minecraft servers. They're considered the gold standard for server performance.

What They Do

• Use the G1 garbage collector instead of Java's default
• Reduce lag spikes caused by garbage collection pauses
• Optimize memory allocation patterns specific to Minecraft's workload
• Prevent the JVM from giving unused memory back to the OS

Applying Aikar's Flags

Via the Startup Tab

1. In the XGamingServer Panel, click Startup
2. Look for a JVM Flags or Additional Java Arguments field
3. Paste the flags below
4. Restart your server

The Flags

For servers with 12GB RAM or less:

-XX:+UseG1GC -XX:+ParallelRefProcEnabled -XX:MaxGCPauseMillis=200 -XX:+UnlockExperimentalVMOptions -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

For servers with more than 12GB RAM: Change these two values:

-XX:G1NewSizePercent=40
-XX:G1MaxNewSizePercent=50

Do They Actually Help?

Yes — measurably. The biggest improvement is reducing TPS lag spikes caused by the JVM pausing to clean up memory. Without these flags, you'll see periodic stutters every few minutes.

Common Mistakes

• Don't over-allocate RAM — giving your server 16GB when it only needs 4GB makes GC pauses worse, not better
• Don't mix GC flags — use Aikar's flags OR other GC settings, not both
• Don't use -XX:+UseConcMarkSweepGC — this is the old CMS collector that Aikar's flags specifically replace

Related Guides

• Performance Optimization
• Server Configuration