OutOfMemoryError: Java Heap Space

What is OutOfMemoryError: Java Heap Space?

The "java.lang.OutOfMemoryError: Java heap space" error occurs when Minecraft runs out of allocated memory (RAM). This is extremely common in modded Minecraft, especially with large modpacks like All The Mods 10 and 11, which require significantly more memory than the default allocation.

Common Error Messages

• "java.lang.OutOfMemoryError: Java heap space"
• "java.lang.OutOfMemoryError: GC overhead limit exceeded"
• "Exception in thread "main" java.lang.OutOfMemoryError"
• "The game crashed whilst rendering overlay - Error: java.lang.OutOfMemoryError: Java heap space"

Why This Happens

Default Allocation is Insufficient

• CurseForge Default: Usually 4GB
• Vanilla Minecraft: Works fine with 2-4GB
• Large Modpacks: Need 8-12GB or more
• ATM10/ATM11: Require minimum 8-10GB to run smoothly

Memory Consumption in Modpacks

How to Fix: Allocate More RAM

Check Your System RAM First

Before allocating RAM to Minecraft:

1. Windows: Open Task Manager (Ctrl + Shift + Esc) → Performance tab → Memory
2. Mac: Apple menu → About This Mac → Memory
3. Important: Don't allocate ALL your RAM to Minecraft

Safe Allocation Guidelines:

CurseForge App

Change RAM Allocation

1. Open CurseForge App
2. Click your Profile Picture (top right)
3. Click Settings
4. Go to Minecraft section
5. Scroll to Java Settings
6. Find Allocated Memory slider
7. Adjust slider to desired amount:
   • ATM10/ATM11: 10GB (10240 MB)
   • Other large packs: 8GB (8192 MB)
8. Click Done
9. Restart any running Minecraft instances

Per-Instance Settings (CurseForge)

You can also set different RAM amounts per modpack:

1. Right-click your modpack in My Modpacks
2. Click Profile Options
3. Enable Override Memory Settings
4. Set Allocated Memory for this pack
5. Click Done

Prism Launcher / MultiMC

Global Settings

1. Open Prism Launcher
2. Click Settings (top right)
3. Go to Java section
4. Check Memory checkbox
5. Set Maximum memory allocation:
   • For ATM10/ATM11: 10240 MB
   • For other packs: 8192 MB
6. Set Minimum memory allocation: 512 MB (leave default)
7. Click OK

Per-Instance Settings

1. Right-click instance
2. Click Edit Instance
3. Go to Settings → Java
4. Check Memory
5. Set Maximum memory allocation
6. Click OK

Official Minecraft Launcher

JVM Arguments Method

1. Open Minecraft Launcher
2. Click Installations tab
3. Click ... (three dots) on your modpack/profile
4. Click Edit
5. Click More Options
6. Find JVM Arguments field
7. Look for -Xmx4G (or similar)
8. Change the number:
   • For 8GB: -Xmx8G
   • For 10GB: -Xmx10G
   • For 12GB: -Xmx12G
9. Click Save
10. Launch game

Example JVM Arguments:

-Xmx10G -Xms512M -XX:+UnlockExperimentalVMOptions 
-XX:+UseG1GC -XX:G1NewSizePercent=20 
-XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 
-XX:G1HeapRegionSize=32M

Only change the -Xmx10G part to your desired RAM amount.

ATLauncher

1. Open ATLauncher
2. Click Settings tab
3. Go to Java/Minecraft section
4. Find Maximum Memory/RAM
5. Enter amount in MB:
   • 8GB = 8192
   • 10GB = 10240
   • 12GB = 12288
6. Click Save

Modrinth App

1. Open Modrinth App
2. Click Settings (gear icon)
3. Go to Java section
4. Set Maximum Memory slider or enter value
5. Apply changes
6. Restart instances

Verifying RAM Allocation

In-Game Check

1. Launch Minecraft
2. Press F3 (debug screen)
3. Look at top-right corner
4. Check Mem: line shows allocated memory
5. Example: "Mem: 45% 4600MB / 10240MB" means 10GB allocated

Task Manager Check

1. Open Task Manager (Ctrl + Shift + Esc)
2. Go to Details tab
3. Find javaw.exe or java.exe
4. Check Memory column
5. Should be close to allocated amount when game is running

Additional Optimization

Java Arguments for Performance

Along with RAM allocation, use these JVM arguments for better performance:

For 10GB RAM allocation:

-Xmx10G -Xms2G -XX:+UnlockExperimentalVMOptions 
-XX:+UseG1GC -XX:G1NewSizePercent=20 
-XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 
-XX:G1HeapRegionSize=32M -XX:+DisableExplicitGC 
-XX:+AlwaysPreTouch -XX:+ParallelRefProcEnabled

Performance Mods

Install these to reduce memory usage:

• FerriteCore: Reduces memory usage by 30-50%
• Memory Leak Fix: Prevents memory leaks
• ModernFix: Multiple optimizations
• Rubidium/Embeddium: Rendering optimization (Forge)
• Sodium: Rendering optimization (Fabric)

Troubleshooting Persistent Issues

Still Getting Errors After Increasing RAM?

• Memory Leak: Some mods may have memory leaks
  • Install Memory Leak Fix mod
  • Restart game every few hours
• Too Much RAM: Allocating too much can cause garbage collection lag
  • Don't exceed 14-16GB even with 32GB+ system RAM
• Wrong Java Version: Ensure correct Java version
  • 1.16 and below: Java 8
  • 1.17-1.20: Java 17 or 21
  • 1.21+: Java 21
• 32-bit Java: Cannot allocate more than 2GB
  • Install 64-bit Java from adoptium.net

Game Stuttering Despite Enough RAM?

• Garbage Collection: Pauses can cause stutters
  • Use G1GC arguments (shown above)
  • Reduce max GC pause time
• Render Distance: Lower to 8-12 chunks
• Graphics Settings: Lower particles, smooth lighting
• Biome Mods: Some cause memory spikes during world generation

Common Mistakes

• Allocating Too Little: 4GB is NOT enough for large modpacks
• Allocating ALL System RAM: Leave 2-4GB for OS
• 32-bit Java: Cannot use more than 2GB
• Wrong JVM Parameter: Using -Xms instead of -Xmx
• Not Restarting Game: Changes require restart
• Multiple Instances Running: Close other launchers/instances

Hardware Upgrade Considerations

When to Upgrade RAM

Consider upgrading system RAM if:

• You have 8GB or less total RAM
• You want to play ATM10/ATM11
• You frequently multitask while gaming
• You experience constant crashes despite proper allocation

Recommended System Specs for Large Modpacks

• Minimum: 16GB system RAM
• Recommended: 32GB system RAM
• CPU: Modern quad-core or better
• Storage: SSD for modpack installation
• GPU: GTX 1060 / RX 580 or better

Modpack-Specific Recommendations

Prevention Tips

• Always Check Requirements: Read modpack description for RAM needs
• Set RAM Before First Launch: Don't wait for crash
• Monitor Memory Usage: Use F3 debug screen
• Install Performance Mods: FerriteCore, ModernFix
• Close Background Apps: Chrome, Discord can use lots of RAM
• Regular Restarts: Restart game every 2-3 hours

Summary

OutOfMemoryError is the most common crash in modded Minecraft and is easily fixed by allocating more RAM. CurseForge and most launchers default to 4GB, but large modpacks like ATM10 and ATM11 need minimum 8-10GB to run properly. Always ensure you have enough system RAM and allocate appropriately!

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