Chunker

• Minecraft 1.20.5+

• Requires Java 21 or higher

Supported Servers:

• Spigot, Bukkit, Paper, Pufferfish, Purpur, Folia

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 region’s position and how many chunks are completed), so crashes have less impact on the generation process.

It works best on Paper forks because it can utilize asynchronous chunk-loading (CompletableFuture) for faster performance. On non-Paper servers (Bukkit/Spigot and others), it falls back to a synchronous chunk-loading method but still performs significantly faster than many default solutions.

You can configure Chunker to run automatically only when there are no players online and to halt immediately if a player joins. This behavior is controlled by auto_run in settings.yml. You can also adjust how aggressively each world’s tasks run by changing task_queue_timer and parallel_tasks_multiplier. If you want to keep the server load minimal, set low concurrency or run only when the server is empty.

Optimized JVM Launch Parameters (start.bat):

@echo off
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:+OptimizeStringConcat -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 server.jar --nogui
pause

• Xms1G and Xmx30G should be updated to match your minimum (Xms) and max memory (Xmx) for your own server.
• Update both XX:ParallelGCThreads and XX:ConcGCThreads to match your number of threads.

Paper Config

Note: On non-Paper servers, asynchronous functionality will not be used.
However, if you are on a Paper-based server (including Pufferfish, Purpur, etc.), you can take extra steps to optimize pre-generation:

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 only uses half your threads for chunk tasks; raising these can help ensure asynchronous chunk generation runs at full speed.
• Lower region-file-cache-size if running pregen on a fresh world with no players online.

Command Usage

The primary commands are:

/pregen <ParallelTasksMultiplier> <PrintUpdateDelay> <world> <Radius or "default">
/pregenoff [world]

Examples

1. /pregen 4 10s world default

   • Pre-generates the overworld (world)
   • Uses 4 parallel chunk-loading tasks (on Paper, these run asynchronously)
   • Prints progress logs every 10 seconds
   • default uses the world border as the radius

2. /pregen 6 5s world 1000b

   • Pre-generates the overworld
   • 6 parallel tasks
   • Prints logs every 5 seconds
   • 1000b = 1000-block radius → Chunker calculates (1000 / 16)²

3. /pregen 2 2m world_nether 500c

   • Pre-generates the Nether
   • 2 parallel tasks
   • Logs every 2 minutes
   • 500c = 500-chunk radius → 500 × 500 = 250,000 chunks

4. /pregen 1 12h world_the_end 100r

   • Pre-generates The End
   • 1 parallel task
   • Logs every 12 hours
   • 100r = 100-region radius → (100 × 32)² = 10,240,000 chunks

Command Parameters

• ParallelTasksMultiplier: Determines how many chunk-loading tasks run in parallel. On Paper, these tasks are async. Recommended: Keep at or below your CPU’s thread count.
• PrintUpdateDelay: How often progress logs appear. Add suffix s, m, or h.
• world: The world to pre-generate. Tab-completion supported.
• Radius: The target radius with a suffix:
  • b – Blocks (e.g., 20000b)
  • c – Chunks (e.g., 500c)
  • r – Regions (e.g., 30r)
  • default – Uses world border
• /pregenoff [world]:
  • No args = stops all worlds
  • With world name = stops that world only

Permissions

(Defaults to OP)

• chunker.pregen – Allows use of /pregen
• chunker.pregenoff – Allows use of /pregenoff
• chunker.* – Grants all Chunker permissions

Configuration: settings.yml

world:
  auto_run: false
  task_queue_timer: 60
  parallel_tasks_multiplier: auto
  print_update_delay: 5s
  radius: default

world_nether:
  auto_run: false
  task_queue_timer: 60
  parallel_tasks_multiplier: auto
  print_update_delay: 5s
  radius: default

world_the_end:
  auto_run: false
  task_queue_timer: 60
  parallel_tasks_multiplier: auto
  print_update_delay: 5s
  radius: default

Summary of Changes from Older Versions

• No more Virtual Threads – Uses standard CompletableFuture concurrency on Paper.
• Improved Schedulers – Custom async scheduler using ForkJoinPool.commonPool().
• Minimal State Tracking – Uses small progress files per world (e.g., world_pregenerator.txt).

Quick Tips

1. Begin with parallel_tasks_multiplier = 1, then adjust.
2. Async loading (Paper and Folia) = much better performance.
3. Use print_update_delay of 10s+ to avoid excessive log output during long runs.