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How to Optimize Minecraft Server Performance with Aikar’s Flags

Aikar’s Flags are JVM startup parameters that improve server performance by optimizing garbage collection and memory management. They reduce lag spikes and provide smoother gameplay. All berrybyte Minecraft servers come with Aikar’s flags by default.
Aikar’s Flags allocates all available memory, so your server may appear to use 100% RAM. This is normal. Install the Spark plugin and run /spark health to see actual usage.

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Setting Up the Flags

Update your server startup command with the flags below. Replace {SERVER_MEMORY} with your RAM amount (e.g., 4096 for 4GB).

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Less than 12GB of RAM

JVM Flags
java -Xms{SERVER_MEMORY}M -Xmx{SERVER_MEMORY}M -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 -jar paper.jar --nogui

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12GB of RAM or more

JVM Flags
java -Xms{SERVER_MEMORY}M -Xmx{SERVER_MEMORY}M -XX:+UseG1GC -XX:+ParallelRefProcEnabled -XX:MaxGCPauseMillis=200 -XX:+UnlockExperimentalVMOptions -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 -jar paper.jar --nogui

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Flag Breakdown

On shared hosting (like berrybyte), leave about 1GB for JVM overhead. This is done automatically.
Key flags:
  • -Xmx / -Xms: Maximum and initial memory (set to same value)
  • -XX:+UseG1GC: Enables G1 garbage collector for better performance
  • -XX:+ParallelRefProcEnabled: Parallel reference processing
  • -XX:MaxGCPauseMillis: Maximum garbage collection pause time
  • -XX:+DisableExplicitGC: Prevents bad plugin code from affecting GC
Remove -XX:+AlwaysPreTouch on Pterodactyl/containerized servers. It can cause crashes by pre-allocating all memory.
Other flags fine-tune G1 garbage collection settings. See Aikar’s blog for detailed explanations. If you have issues, check server.log for error messages.

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Common Issues

Server shows 100% RAM usage
  • Normal behavior - flags allocate all available memory
  • Fix: Use Spark plugin and run /spark health for actual usage
Server crashes with “Cannot allocate memory”
  • Usually caused by -XX:+AlwaysPreTouch in containers
  • Fix: Remove -XX:+AlwaysPreTouch flag
Poor performance
  • Incorrect memory allocation or wrong Java version
  • Fix: Use Java 11+ and leave 1GB for JVM overhead
Need help? Ask in our Discord. Consider donating to Aikar if these flags helped your server.