Memory allocation errors are among the most common Minecraft server issues. This guide helps you properly configure RAM settings and resolve memory-related crashes.

Understand Memory Error Types

Identify which memory issue you're experiencing:

Common Memory Errors:

java.lang.OutOfMemoryError: Java heap space - Not enough allocated RAM
Could not reserve enough space - System lacks available memory
GC overhead limit exceeded - Too much time spent garbage collecting
Metaspace error - Class metadata space exhausted
Direct buffer memory - Native memory allocation failed

Symptoms of Memory Issues:

Server crashes during startup or operation
Extreme lag and poor TPS (ticks per second)
Chunk loading failures
Players getting kicked with timeout errors
Console spam about memory warnings

Check Current Memory Settings

Analyze your current RAM allocation:

Find startup script: Look for start.sh, start.bat, or run.bat
Check Java arguments: Look for -Xmx and -Xms values
Verify system RAM: Ensure you have enough physical memory
Monitor usage: Use task manager or htop to check RAM usage

Common startup arguments:

java -Xms2G -Xmx4G -jar server.jar nogui

-Xms2G = Initial memory (2GB)
-Xmx4G = Maximum memory (4GB)

Calculate Proper RAM Allocation

Determine optimal memory settings for your server:

RAM Recommendations by Server Type:

Vanilla (1-10 players): 2-3GB
Vanilla (10-20 players): 3-4GB
Lightly modded: 4-6GB
Heavily modded: 6-8GB minimum
Large modpacks: 8-12GB or more

System RAM Guidelines:

Never allocate more than 75% of system RAM
Leave at least 2GB for the operating system
Account for other running applications
Consider overhead for Java garbage collection

Allocating too much RAM can cause performance issues. More is not always better!

Fix Startup Memory Errors

Resolve "Could not reserve enough space" errors:

Reduce allocation: Lower -Xmx value to available RAM
Close other programs: Free up system memory
Use 64-bit Java: 32-bit Java limited to ~1.5GB
Check virtual memory: Ensure adequate swap/page file
Restart system: Clear memory fragmentation

Example fix for 8GB system:

# Before (fails)
java -Xms8G -Xmx8G -jar server.jar

# After (works)
java -Xms2G -Xmx6G -jar server.jar

Optimize Java Arguments

Use advanced JVM flags for better memory management:

Recommended Arguments for Minecraft:

java -Xms4G -Xmx4G -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 
-jar server.jar nogui

Key Flags Explained:

UseG1GC: Modern garbage collector for large heaps
ParallelRefProcEnabled: Parallel reference processing
MaxGCPauseMillis: Target maximum GC pause time
AlwaysPreTouch: Pre-allocate memory at startup

Fix OutOfMemoryError During Operation

Address memory errors that occur while server is running:

Increase -Xmx: Add more maximum memory if available
Reduce view distance: Lower in server.properties
Limit entities: Use plugins to cap mob spawning
Clear ground items: Remove dropped items regularly
Optimize chunks: Pre-generate world to reduce load
Remove memory leaks: Update or remove problematic plugins/mods

Quick fixes in game:

/kill @e[type=item]  # Remove all dropped items
/worldborder set 5000  # Limit world size
/gamerule maxEntityCramming 24  # Limit entity stacking

Monitor Memory Usage

Track memory consumption to prevent issues:

Monitoring Commands:

/memory: Shows current memory usage (some servers)
/tps: Check server performance metrics
/timings: Detailed performance analysis (Paper)
F3 debug: Client-side memory display

External Monitoring Tools:

htop/Task Manager for system memory
Java VisualVM for JVM monitoring
Spark plugin for in-game profiling
Pterodactyl panel memory graphs

Special Cases and Solutions

Handle specific memory-related scenarios:

Modded Server Memory:

Some mods have memory leaks - identify and report
Use FoamFix or VanillaFix for optimization
Allocate 1-2GB extra for mod overhead
Consider using performance mods

32-bit System Limitations:

Maximum ~1.5GB allocation possible
Upgrade to 64-bit OS and Java
Use lightweight server software
Limit world size and players

Shared Hosting Limits:

Cannot exceed plan's RAM limit
Optimize within constraints
Consider upgrading hosting plan
Use performance-focused configs

Prevent Future Memory Issues

Best practices for long-term stability:

Regular restarts: Schedule daily restarts to clear memory
Update regularly: Keep server software and plugins current
Monitor growth: Track memory usage trends
Plan for expansion: Upgrade before hitting limits
Optimize continuously: Review and adjust settings
Document settings: Keep notes on what works

Proper memory allocation is crucial for server stability. Start conservative and increase gradually while monitoring performance.

How to Fix Memory Allocation Errors