Chunker - Official Support & Downloads

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Contributions

PRs welcome

This repository is public. Fork the repo, create a branch, and open a pull request. I will merge changes that work and do not introduce issues. If I need changes I will leave feedback.

Quick checklist:

• Link the related issue if any.
• Add a short description and steps to test.
• Build must pass with mvn clean package using Java 25.

Supported MC Versions

• Target version: 26.1.2
• Requires Java 25
• Older Java 21 / pre-26.1.2 server builds are no longer supported by 26.1.2 and newer

Supported Servers

• Paper
• Folia
• Paper-compatible forks such as Pufferfish, Purpur, and Leaf

Chunker still has fallback logic for non-Paper server paths, but the current plugin baseline is built for the 26.1.2 API and Java 25.

Overview

Chunker is designed to be more efficient and resilient than traditional pre-generators. Many pre-generators track thousands of chunks in memory, risking significant rollback or data loss if the server crashes. Chunker, by contrast, only tracks minimal state like the current iterator position, submitted progress, completed progress, and the generation center, so crashes or restarts have less impact on the generation process.

Chunker works best on Paper and Paper forks because it can use asynchronous chunk-loading through CompletableFuture. Folia uses its region scheduler path. On non-Paper server paths, Chunker falls back to synchronous loading behavior.

You can configure Chunker to run automatically only when there are no players online and to halt if a player joins. This behavior is controlled by auto_run in settings.yml. You can also adjust how aggressively each dimension runs by changing task_queue_timer and parallel_tasks_multiplier.

Optimized JVM Launch Parameters (start.bat)

@echo off
for %%f in (*.jar) do set JAR=%%f
REM Launching Java with Aikar-style flags
java ^
 -Xms1G ^
 -Xmx30G ^
 -XX:+UseG1GC ^
 -XX:+UnlockExperimentalVMOptions ^
 -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 ^
 -XX:+UseCompressedOops ^
 -XX:+DisableExplicitGC ^
 -XX:+AlwaysPreTouch ^
 -XX:+ParallelRefProcEnabled ^
 -XX:+UseNUMA ^
 -XX:ParallelGCThreads=16 ^
 -XX:ConcGCThreads=16 ^
 -XX:MaxGCPauseMillis=50 ^
 -Dusing.aikars.flags=https://mcflags.emc.gs ^
 -Daikars.new.flags=true ^
 -jar "%JAR%" --nogui
pause

• Xms1G and Xmx30G should be updated to match your server's minimum and maximum memory.
• Update both XX:ParallelGCThreads and XX:ConcGCThreads to match your CPU thread count.

Paper Config

Note: On non-Paper servers, Paper async chunk functionality will not be used. On Paper-based servers, you can tune chunk generation and I/O parallelism for better pre-generation throughput.

In your paper-global.yml or equivalent, consider increasing the parallelism for chunk generation and I/O:

chunk-loading-advanced:
  auto-config-send-distance: true
  player-max-concurrent-chunk-generates: -1
  player-max-concurrent-chunk-loads: -1

chunk-loading-basic:
  player-max-chunk-generate-rate: -1.0
  player-max-chunk-load-rate: -1.0
  player-max-chunk-send-rate: -1.0

chunk-system:
  gen-parallelism: default
  io-threads: 16
  worker-threads: 16

region-file-cache-size: 16

• Adjust io-threads and worker-threads to match or approach your CPU's thread count.
• By default, Paper may not use all available CPU threads for chunk work.
• Lower region-file-cache-size if running pre-generation on a fresh world with no players online.

Command Usage

The primary commands are:

/pregen <ParallelTasksMultiplier> <PrintUpdateDelay> <dimension> <Radius or "default"> [safety]
/pregenoff [dimension]
/pregen reset <dimension>

Examples

1. /pregen 4 10s minecraft:overworld default

   • Pre-generates the overworld.
   • Queues 4 chunk-loading tasks per scheduler cycle.
   • Prints progress logs every 10 seconds.
   • default uses the world border as the radius.

2. /pregen 6 5s minecraft:overworld 1000b

   • Pre-generates the overworld.
   • Queues 6 tasks per scheduler cycle.
   • Prints logs every 5 seconds.
   • 1000b means a 1000-block radius, rounded to full region coverage.

3. /pregen 16 5s minecraft:the_nether 2r safety

   • Pre-generates the Nether.
   • Queues safety-mode work in parallel using the 16 multiplier.
   • Prints logs every 5 seconds.
   • 2r means a 2-region radius, rounded to full region coverage.
   • safety forces the more conservative urgent async generation path.

4. /pregen 1 12h minecraft:the_end 100r

   • Pre-generates The End.
   • Queues 1 task per scheduler cycle.
   • Logs every 12 hours.
   • 100r means a 100-region radius.

5. /pregen reset minecraft:the_nether

   • Deletes saved pre-generation progress for the Nether.

Command Parameters

• ParallelTasksMultiplier: Determines how many chunk-loading tasks are queued per scheduler cycle. On Paper, these tasks use async chunk APIs. Higher values can increase throughput but also increase CPU, memory, and disk pressure.
• PrintUpdateDelay: How often progress logs appear. Add suffix s, m, or h.
• dimension: The dimension to pre-generate. Use canonical namespaced keys such as minecraft:overworld or minecraft:the_nether. Tab completion is supported.
• Radius: The target radius with a suffix:
  • b - Blocks, for example 20000b
  • c - Chunks, for example 500c
  • r - Regions, for example 30r
  • default - Uses the world border
• safety: Optional. Forces the conservative urgent async safety path on Paper.
• /pregenoff [dimension]:
  • No args = stops all active pre-generation tasks.
  • With a dimension key = stops that dimension only.

Permissions

Defaults to OP.

• chunker.pregen - Allows use of /pregen
• chunker.pregenoff - Allows use of /pregenoff
• chunker.reset - Allows use of /pregen reset <dimension>
• chunker.* - Grants all Chunker permissions

Configuration: settings.yml

# World Configuration for Chunker Plugin

# auto_run: Set to true if you want pre-generation to start automatically when no players are on the server.
# Acceptable values: true or false

# task_queue_timer: Determines how fast chunks are queued up. A value between 50-70 is recommended for modern AMD 5000 series and Intel 13th Gen CPUs in the Overworld.
# Adjust based on performance needs.

# parallel_tasks_multiplier: Sets how many async tasks are queued per scheduler cycle. 'auto' will distribute tasks based on your thread count for auto-run.
# You can also set a specific integer value. Higher values increase load.

# print_update_delay: How often to print information (s-Seconds, m-Minutes, h-Hours). Default is 5s.

# radius: Defines how far the pre-generator should run (b-Blocks, c-Chunks, r-Regions) or 'default' to pre-generate until the world border.

# Optional command safety mode:
# Add 'safety' after the radius to force Chunker's urgent async safety generation path on modern versions.
# Example: /pregen 4 5s minecraft:overworld 5r safety
# This keeps progress tied to completed chunks while still queuing safety work in parallel.

# center: Sets where the pregen spiral starts.
# - 'default' uses the world border center, or the world spawn if no border center is set.
# - '~ ~' always uses the current world spawn.
# - 'x z' uses fixed block coordinates, for example: "0 0" or "1500 -500".

minecraft:overworld:
  center: default
  auto_run: false
  task_queue_timer: 60
  parallel_tasks_multiplier: auto
  print_update_delay: 5s
  radius: default

minecraft:the_nether:
  center: default
  auto_run: false
  task_queue_timer: 60
  parallel_tasks_multiplier: auto
  print_update_delay: 5s
  radius: default

minecraft:the_end:
  center: default
  auto_run: false
  task_queue_timer: 60
  parallel_tasks_multiplier: auto
  print_update_delay: 5s
  radius: default

Quick Tips

1. Begin with a lower ParallelTasksMultiplier, then adjust upward while watching CPU, memory, and disk usage.
2. Paper and Folia paths provide much better performance than synchronous Bukkit-style loading.
3. Use print_update_delay of 10s or longer to avoid excessive log output during long runs.
4. Use safety only when you want the more conservative Paper generation path; omit it for maximum speed.