Minecraft - High CPU usage and slow chunk loading on modded server

Technical Support
, ,
1

System Information

CPU Model AMD EPYC 9354P 32-Core Processor
Field Value
Operating System Linux - Debian GNU/Linux 12 on x86_64
Product AMP ‘Phobos’ v2.6.3.2 (Mainline)
Virtualization Docker
Application Minecraft
Module MinecraftModule
Running in Container Yes
Current State Ready

Task

Trying to diagnose and resolve severe CPU usage and chunk loading lag on our Craftoria NeoForge server

Problem Description

Issue

We’ve noticed that our server’s CPU usage spikes to 100% whenever chunks are being loaded — especially when flying quickly through the world using spells or jetpacks. As more players join (up to four), the issue becomes significantly worse.
It seems like the CPU simply can’t handle the chunk generation and loading properly, causing heavy lag and extremely slow terrain updates.
Since Craftoria is a rather demanding modpack, we understand some performance impact is normal — but this looks excessive.

Reproduction Steps

  • Joined the server with one player and began flying through unexplored terrain using jetpacks and/or teleportation spells.
  • Observed CPU usage reaching 100% during chunk generation and rendering, causing severe lag and slow chunk loading.
  • Repeated the same test with up to four players — performance degraded further, with the same high CPU usage behavior.
  • Reduced both render and simulation distance settings, but this had no noticeable impact on performance.
2

This is pretty normal with modded MC, chunk generation/loading is a pretty expensive operation, most of which is handled on one core/thread.
You might want to check that your server-side render distance is set to something reasonable (the default is 10), and check that Use Synchronous IO is disabled in the MC instance’s settings.