chestloaders

chestloaders is a Minecraft 1.21.8+ datapack that adds a simple and lag-friendly chunk loading system for chest minecarts. It utilises /forceload to load a 3x3 of entity-processing chunks around the cart, much akin to Nether Portal loading—but on rails!

Algorithm

• Every second carts moving @ ≥ 1 m/s get a 3x3 chunk area loaded
  • Carts marked for unloading don't get re-force loaded
• Every 15 seconds, all chunks without a cart nearby that was just force loaded above are unloaded
• Every 60 seconds, all carts that have moved ≤ 15 m in the last minute are scheduled to be checked again
  • After 60 seconds from being scheduled:
    • If the cart moved ≥ 16 m in the last minute, its schedule is cancelled
    • If not, then the cart is promoted to be fully marked for unloading. The chunks around it will be unloaded in the range of 1–15 seconds from now

Note

The distance a cart moved in a minute is an important check for the logic of determining which carts shouldn't be loaded, in order to prevent lag. It is calculated as:
$$\mathrm{delta_pos}(x, y, z) \coloneqq \left|x_\mathrm{new} - x_\mathrm{old}\right| + \left|y_\mathrm{new} - y_\mathrm{old}\right| + \left|z_\mathrm{new} - z_\mathrm{old}\right|$$

Note that this is using the X/Y/Z coordinates, and not velocity maths. Therefore, a cart can travel 300 m around a circular track (for example), but this track must cross over ~16 blocks in at least one axis. This prevents carts travelling in a small circle or in machines from being used as chunkloaders, thus only permitting long-distance-travelling carts.

Installing

1. Download the code as a ZIP using that link or by hitting Code → Download ZIP above
2. Extract the ZIP to your world or server's <world name>/datapacks/ folder. The ZIP will contain a folder called chestloaders-main/, and inside that will be pack.mcmeta, data/, etc: you want chestloaders-main/ to be directly under the datapacks/ folder, i.e. the pack.mcmeta will be inside <world name>/datapacks/chestloaders-main/
3. In game, run /datapack enable "file/chestloaders-main". That's it!
   • chestloaders will run automatically upon every world load/server boot. There's nothing you need to do in-game to get it to start chunk loading carts

Removing

1. Run /function chestloaders:unload as opposed to /datapack disable ... to remove all scoreboards created, etc. The unload function will disable the datapack itself automatically, and will also tidy up tags and scoreboards created
2. Delete the chestloaders-main/ folder inside <world name>/datapacks/

Note

The unload function removes the following tags from all entities:

• chestloaders.scheduled_unload
• chestloaders.unload
• chestloaders.just_unloaded

It uses @e to do this. Generally, if a cart has these tags, it's because it's loaded. The only time a cart will have these tags and be unloaded is if the server restarted or crashed whilst a cart was chunk loading. Tags do not inherently cause any performance issues, however they do take up space in entity NBT and if you want to be 100% rid of chestloaders for whatever reason, do note that these tags cannot be automatically removed by the unload function if the carts with the tags in question aren't loaded in.