Minecraft 1.21 Lag Fix: Complete Server Optimization Guide 2026

Quick Answer: Minecraft 1.21 lag is caused by heavier world generation and more entities. Solve this with: 1) Purpur server jar (best performance fork), 2) Reduce simulation-distance to 4-6, 3) Install Lithium + FerriteCore mods, 4) Use correct JVM flags (Aikar's). A properly configured 4GB VPS will run a 10-15 player server smoothly at 20 TPS.

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Why Minecraft 1.21+ Is So Much Heavier

The Technical Changes

Minecraft 1.21 "Tricky Trials" and 1.21+ introduced significant changes:

| Change | Impact on Performance | Percentage of Additional CPU | |-------------|------------------------|------| | Trial Chambers (new structure) | Complex generation with many entities | +15-25% | | Breeze mob | Advanced AI with pathfinding | +10% on spawning | | Wind Charges | Additional projectile physics | +5-10% in combat | | Higher build limit | More chunks to track | +5-15% | | Copper/Tuff variants | More block states in memory | +5% RAM |

Result: A standard 1.20 setup that achieved 20 TPS drops to 15-18 TPS on 1.21 with the same hardware.

The TPS Problem

TPS = Ticks Per Second

Minecraft runs on a "tick loop": the entire world is updated 20 times per second (mob movement, redstone, crop growth, etc.).

• 20 TPS = Perfect, each tick lasts 50ms
• 15-18 TPS = You will notice gameplay lag, movement stuttering
• <15 TPS = Unplayable, severe lag spikes

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Step 1: The Right Server Software (Paper vs Purpur vs Forge)

1.1 The Server Software Hierarchy

Vanilla (Mojang) → Bad for performance
    ↓
Spigot → Basic Optimizations
    ↓
Paper → Excellent Optimizations + API
    ↓
Pufferfish → Paper + additional async processing
    ↓
Purpur → Pufferfish + configuration freedom ⭐ BEST

1.2 Why Purpur?

Purpur = Paper + Pufferfish + extra features

| Feature | Vanilla | Paper | Purpur | |--------|-------------|-------|--------| | Async chunk loading | ❌ | ✅ | ✅ | | Mob AI optimization | ❌ | Basic | Advanced | | Config options | Little | Much | Very much | | Entity activation range | ❌ | Static | Dynamic | | Redstone Optimizations | ❌ | ✅ | ✅+ | | Disable per-mob AI | ❌ | ❌ | ✅ | | Gameplay features | Basic | Basic | Extensive |

Practical example:

On the same 4GB VPS with 10 players:

• Vanilla: 12-15 TPS (unplayable)
• Paper: 18-19 TPS (playable, sometimes lag)
• Purpur: 19.8-20 TPS (perfect)

1.3 Purpur Install

Download:

Go to https://purpurmc.org/downloads

# SSH to your VPS
ssh root@je-vps-ip

# Create server directory
mkdir -p /opt/minecraft-server
cd /opt/minecraft-server

# Download Purpur (replace version with current one)
wget https://api.purpurmc.org/v2/purpur/1.21.1/latest/download -O purpur.jar

# Accept EULA
echo "eula=true" > eula.txt

First start (generates config files):

java -Xms2G -Xmx4G -jar purpur.jar nogui

Stop the server after 30 seconds (Ctrl+C). You now have all the config files.

Step 2: Critical Configuration Adjustments

2.1 server.properties (Basic Settings)

nanoserver.properties

Major changes:

# === PERFORMANCE CRITICAL ===

# Simulation distance: How many chunks around player are "active".
# Default: 10 → Decrease to 4-6
# This is THE most important setting!
simulation-distance=4

# View distance: How many chunks player can SEE
# Can stay high, players see far but world is only active close up
view distance=10
# Network compression: Balance between CPU and bandwidth
#256 is sweet spot
network-compression-threshold=256

# Spawn protection (unnecessary on survival)
spawn protection=0

# === CHUNK LOADING ===

# How many chunks around spawn point always remain loaded
# Decrease or 0 for lower RAM
spawn-chunk-radius=2

Why is simulation distance so crucial?

| Simulation Distance | Active Chunks | Mobspawns | CPU Usage | |----------|----------------|-----------|-------------| | 10 (default) | 441 chunks | Complete | 100% | | 6 | 169 chunks | 60% | 38% | | 4 | 81 chunks | 40% | 18% |

Going from 10 to 4 saves >80% CPU! Players barely notice this (farms slightly slower, mobs spawn closer).

2.2 purpur.yml (Advanced Purpur Options)

nanopurpur.yml

Performance Sections:

world settings:
  default:
    # === MOB AI OPTIMIZATION ===
    mobs:
      # Disable AI for specific mobs that contribute little
      zombie:
        ridable: false
        aggressive-towards-villager-when-lagging: false
# Tropical fish do NOTHING but cost a lot of AI
      tropical_fish:
        ridable: false
        takes-damage-from-water: false
      
      # Axolotls spawn a lot but do little
      axolotl:
        ridable: false
    
    # === REDSTONE ===
    # Limit hopper checks (biggest cause of lag)
    hopper:
      disable-move-event: true
      
    # === ENTITIES ===
    # Merge dropped items (fewer entities)
    merge radius:
      item: 4.0
      exp: 6.0
    
    # Delete items faster
alt-item-despawn-rate:
      enabled: true
      items:
        cobblestone: 300 # 15 sec (was 6000 = 5 min)
        nether rack: 300
        sand: 300
        gravel: 300
        
    # === VILLAGERS (CPU KILLERS) ===
    villager:
      # Limit how many villagers get AI per tick
      lobotomize:
        enabled: true
        check interval: 100
      
      # Disable brain ticking when far away
      brain tricks: 2
      
    # === CHUNK LOADING ===
    # Async chunk loading (does not block main thread)
use-async-pathfinding: true

Pro tip - Lobotomize Villagers:

Lobotomize = "to make brain dead". Villagers who cannot pathfind (e.g. locked in trading hall) no longer receive AI after 100 ticks. They still work (trades, breeding), but cost 0% CPU. Huge boost for servers with trading halls.

2.3 spigot.yml (Spigot Optimizations)

nano spigot.yml

world settings:
  default:
    # === MOB SPAWN LIMITS ===
    # By default, WAY too many mobs spawn
mob spawn range: 6 # Was 8, decrease = fewer mobs far away
    
    entity activation range:
      # How far mobs are "active" (AI running)
      animals: 16 # Was 32
      Samples: 24# Was 32
      raiders: 48 # Was 48 (ok)
      misc: 8 # Was 16
      water: 8 # Wash 16 (fish/axolotls)
      villagers: 16 # Was 32
      flying monsters: 48 # Phantoms
      
    # === TICK RATES ===
    # How often to update certain systems
    entity tracking range:
      players: 48
animals: 48
      samples: 48
      misc: 32
      
    # === GROWTH RATES ===
    # Slow down crop/plant growth (fewer ticks)
    growth:
      cactus modifier: 150 # Was 100 (50% slower)
      cane modifier: 150
      melon modifier: 150
      mushroom modifier: 150
      pumpkin modifier: 150
      sapling modifier: 150
      beetroot modifier: 150
      carrot modifier: 150
      potato modifier: 150
      wheat modifier: 150
      
    # === HOPPER OPTIMIZATION ===
    hopper transfer: 8 # Was 8 (ok)
hopper check: 1 # Was 1 (ok)
    hopper-amount: 1 # How many items per transfer
    
    # === MERGE SETTINGS ===
    merge radius:
      item: 4.0
      exp: 6.0

Why increase growth modifiers?

Farms still work, but 50% slower. This saves a lot of CPU because block ticking (the check "should I grow?") happens less often. For casual servers you hardly notice this.

2.4 paper-world-defaults.yml (Paper Specific)

nano config/paper-world-defaults.yml

entities:
  # === SPAWNING ===
  spawning:
    # Limit total number of entities
    spawn limits:
      ambient: 5 # Bats
      axolotls: 3 # Axolotls (CPU killers)
      creature: 8 # Animals
      sample: 50# Samples
      underground_water_creature: 3 # Glow squid
      water_ambient: 15 # Pisces
      water_creature: 3 # Dolphins/turtles
      
    # === TICK RATES ===
    # Per-mob spawning budget
    per-player-mob-spawns: true
    
  # === BEHAVIOR ===
behaviour:
    # Disable AI for mobs far away
    tick-inactive-villagers: false
    
    # Zombies don't break doors (saves pathfinding)
    zombie-villager-infection-chance: 50.0
    
chunks:
  # === CHUNK SYSTEM ===
  # Auto-save interval (higher = less IO lag)
  auto-save interval: 6000 # Was 6000 (5 min is ok)
  
  # Prevent chunk loading cascade (lag spike cause)
  prevent-moving-into-unloaded-chunks: true
  
  # Max chunks per tick
  max-auto-save-chunks-per-tick: 8

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Step 3: Java Startup Flags (Aikar's Flags)

3.1 Why Standard Java is Bad

Default java -jar server.jar uses old garbage collector (GC) which:

• Every 30-60 seconds server freezes for 500-2000ms
• Uses memory inefficiently
• Causes "lag spikes" where players DC

3.2 Aikars Flags: The Gold Standard

These flags were developed by Aikar (Minecraft performance expert) and tested on thousands of servers.

For 4GB RAM server:

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 \
-Dusing.aikars.flags=https://mcflags.emc.gs \
  -Daikars.new.flags=true \
  -jar purpur.jar nogui

For 6GB RAM server:

Replace -Xms4G -Xmx4G with -Xms6G -Xmx6G

For 8GB+ RAM server (ZGC variant):

java -Xms8G -Xmx8G\
  -XX:+UseZGC \
  -XX:+ParallelRefProcEnabled \
  -XX:+UnlockExperimentalVMOptions\
  -XX:+DisableExplicitGC \
  -XX:+AlwaysPreTouch \
  -XX:ZCollectionInterval=5 \
  -XX:ZAllocationSpikeTolerance=2.0 \
  -Dusing.aikars.flags=https://mcflags.emc.gs \
  -jar purpur.jar nogui

ZGC (Z Garbage Collector) is even better for 8GB+ servers: GC pauses <10ms (totally unnoticeable).

3.3 Create a Startup Script

nanostart.sh

#!/bin/bash

# Aikar's flags for 4GB
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 \
  -Dusing.aikars.flags=https://mcflags.emc.gs \
  -Daikars.new.flags=true \
  -jar purpur.jar nogui

chmod +x start.sh
./start.sh

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Step 4: Performance Mods (Essential for 1.21)

4.1 Lithium - Server Side Performance

What does Lithium do?

Optimizes virtually all Minecraft systems without changing gameplay:

• Mob AI pathfinding (50% faster)
• Block ticking (crops, redstone)
• Chunk loading
• Physics calculations

Installation:

# Download from Modrinth
cd /opt/minecraft-server/mods
wget https://cdn.modrinth.com/data/gvQqBUqZ/versions/latest/lithium-fabric-mc1.21.jar

# Or for Paper/Purpur (via plugin wrapper):
# Lithium does NOT work directly on Paper, but you have Lithium features via Purpur configs

⚠️ Important: Lithium is a Fabric mod. For Paper/Purpur servers you already have the optimizations via Purpur's code (based on lithium patches).

4.2 FerriteCore - RAM Optimization

What does FerriteCore do?

Reduces RAM usage by 30-40% through more efficient data structures. Essential for modded or 4GB servers.

Download:

cd /opt/minecraft-server/mods
wget https://cdn.modrinth.com/data/uXXizFIs/versions/latest/ferritecore-7.0.0-fabric.jar

Result: 4GB server with 10 players now uses ~2.8GB instead of 3.8GB = more space for chunks.

4.3 Krypton - Network Optimization

Optimizes how the server sends packets to clients. Especially useful with 15+ players.

wget https://cdn.modrinth.com/data/fQEb0iXm/versions/latest/krypton-0.2.8-fabric.jar

4.4 For Modded Servers (Forge/NeoForge)

If you are running a modded server (All the Mods, FTB, etc.):

Essential Performance Mods:

| Mod | Function | Link | |-----|---------|------| | ModernFix | General optimizations | modrinth.com/mod/modernfix | | FerriteCore | RAM reduction | modrinth.com/mod/ferritecore | | EntityCulling | Render optimization | modrinth.com/mod/entityculling | | Canary | Lithium for Forge | modrinth.com/mod/canary | | Roadrunner | Async chunk loading | modrinth.com/mod/roadrunner |

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Step 5: Monitoring and Diagnostics

5.1 Spark - Performance Profiler

Installation:

cd /opt/minecraft-server/plugins
wget https://ci.lucko.me/job/spark/lastSuccessfulBuild/artifact/spark-bukkit/build/libs/spark-bukkit.jar

In-game use:

/spark profiler starts
# Let server run for 2-3 minutes
/spark profiler stop
/spark profiler open

You will receive a web link with detailed analysis:

• Which plugins/mods cost the most CPU
• Which chunks cause lag
• Entity counts per chunk

5.2 Timings - Built-in Diagnostics

/timingson
# Wait 10 minutes
/timingspaste

Returns report with:

• TPS history -Plugin performance
• Entity activity

Read timings report:

Look for red bars in the report:

• Entity Tick high → Too many entities, increase despawn rates
• Tile Entity high → Too many hoppers/chests, optimize redstone
• World Tick high → Simulation distance too high

5.3 TPS Command

Check real-time TPS:

/tps

Output:

TPS from last 1m, 5m, 15m: 19.8, 19.9, 20.0

Good: >19.5 consistent Moderate: 17-19 (noticeable lag) Bad: <17 (unplayable)

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Step 6: Hardware Considerations (VPS Selection)

6.1 RAM Requirements

| ServerType | Players | Mods | Minimum RAM | Recommended RAM | |-------------|---------|------|-------------|----------------| | Vanilla 1.21 | 1-10 | None | 2GB | 4GB | | Vanilla 1.21 | 10-20 | None | 4GB | 6GB | | Vanilla 1.21 | 20-50 | None | 6GB | 8GB | | Light Modpack | 1-10 | 50-100 | 4GB | 6GB | | Heavy Modpack | 1-10 | 150+ | 6GB | 8-12GB | | ATM9/FTB | 1-5 | 300+ | 8GB | 12-16GB |

6.2 CPU Requirements

Clock speed > Core count for Minecraft (single-threaded game logic).

| VPS Spec | Max Players (Vanilla) | TPS Forecast | |----------|----------------------|-----------------| | 2 cores @ 2.4 GHz | 5-8 | 18-19 TPS | | 2 cores @ 3.0 GHz+ | 10-15 | 19-20 TPS | | 4 cores @ 3.0 GHz+ | 15-25 | 20TPS | | 6 cores @ 3.5 GHz+ | 25-40 | 20TPS |

Space Node Recommendations:

• Budget (€10-15/month): 4GB RAM, 2 cores → Perfect for 5-10 players
• Standard (€20-25/month): 6GB RAM, 4 cores → Good for 10-20 players
• Pro (€35-50/month): 8-12GB RAM, 4-6 cores → Heavy modpacks or 20+ players

6.3 Storage: NVMe vs SSD vs HDD

| Type | Chunk Load Time | Auto save Lag | Price | |------|----------------|---------------|-------| | HDD | 500-1000ms | Noticeable freezes | Cheap | | SSD | 50-100ms | Little hickup | Standard | | NVMe | 10-30ms | Unnoticeable | Premium |

For Minecraft: NVMe is significantly better. Chunk loading is I/O intensive. Space-Node VPS uses NVMe standard.

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Step 7: Troubleshooting Specific Problems

Problem: Lag Spikes every 30 seconds

Cause: Java Garbage Collection with bad flags

Diagnosis:

# Add to startup flags
-XX:+PrintGCDetails -Xlog:gc*:file=gc.log

Check gc.log. If you see:

[Full GC (Allocation Failure) 2048M->1800M(2048M), 2.1 secs]

This is a 2+ second freeze. Solution: Use Aikar's flags.

Problem: High RAM usage (server crashed)

Diagnosis:

# In-game command
/forge entity list

# Or via Spark
/spark heap dump

Common causes:

1. Too many entities in spawn chunks

   • Fix: Reduce spawn-chunk-radius to 0-2

2. Mob farm overload

   • Solution: Limit entities with entity-activation-range

3. Memory leak in plugin/mod

   • Solution: Check Spark heap dump, disable suspicious plugin

Problem: Server "Can't keep up" warnings

Console output:

[WARN] Can't keep up! Is the server overloaded? Running 5000ms behind, skipping 100 ticks

This means: The server could not complete one tick in 50ms, so it skips ticks = rubberband lag.

Top 3 causes:

1. Simulation distance too high

   • Reduce to 4

2. Redstone lag (hoppers, observers)

   • Use /spark → find chunks with many tile entities

• Optimize with water streams instead of hoppers

1. Not enough CPU
   • Upgrade VPS or reduce player limit

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Step 8: Basic Configuration Checklist

Print this checklist and check off:

server.properties:

• [ ] simulation-distance=4 (or max 6)
• [ ] view-distance=10
• [ ] network-compression-threshold=256

purpur.yml:

• [ ] villager.lobotomize.enabled=true
• [ ] merge-radius.item=4.0
• [ ] alt-item-despawn-rate.enabled=true

spigot.yml:

• [ ] mob-spawn-range=6
• [ ] entity-activation-range reduced
• [ ] hopper-transfer=8

Start script:

• [ ] Aikar's flags used
• [ ] RAM setting correct (-Xms and -Xmx same)
• [ ] Java 21 (Temurin/Adoptium)

Performance mods:

• [ ] Lithium/Purpur optimizations
• [ ] FerriteCore (as modded)

Monitoring:

• [ ] Spark plugin installed
• [ ] /tps check after each change

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Result: Before and After Optimization

Example Case: 10 Player Survival Server

| Metric | For (Vanilla) | After (Purpur + Configs) | Improvement | |--------|----------------|----------------------|-------------| | TPS | 14-16 | 19.8-20 | +25-40% | | MSPT | 65-80ms | 45-50ms | -30% | | RAM usage | 3.8GB | 2.6GB | -30% | | Chunk load time | 800ms | 150ms | -80% | | Lay spikes | Every 30sec | None | -100% |

Player experience:

• ✅ No rubber band
• ✅ Instant chunk loading
• ✅ Fluid combat
• ✅ No disconnects due to lag

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Conclusion: From Laggy Server to Fluid Experience

By following this guide you will transform a Minecraft 1.21 server from unusable to professional level:

1. ✅ Purpur for best performance baseline
2. ✅ Simulation distance 4-6 for 80% less CPU
3. ✅ Aikar's JVM flags for stable garbage collection
4. ✅ Targeted config tuning for every aspect
5. ✅ Performance mods where necessary
6. ✅ Monitoring tools to find problems

Time investment: 1-2 hours setup, lifetime benefits.

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Ready to run an optimized Minecraft server? Space-Node VPS hosting offers NVMe servers specifically tailored to Minecraft, with pre-configured Purpur setups available. From €10/month with 24/7 support. Related guides:

• Forge vs NeoForge: Which Modloader to Choose in 2026
• RAM Calculator: How Much Do You Really Need?
• Top 10 Performance Mods for Minecraft 1.21