No Unused Chunks

This Minecraft mod reduces world size by discarding unused chunks. In other words, any newly generated chunks that the player or an entity or a block hasn’t interacted with will not be saved, and that will therefore reduce the world size. Works in both singleplayer and on dedicated Minecraft servers.

Important: Please back-up your world if you are planning on using this mod on an already existing world. This mod shouldn’t cause any issues, but it is still a good idea to back-up worlds, just in case. Also, Mod Menu and Cloth Config API are optional dependencies.

How does the mod work?

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Every chunk in a world has a special flag called “needs saving”. The game uses this flag to keep track of whether any changes were made to a chunk. When this flag is set to “true”, the game will then save the chunk the moment it gets unloaded. The game does this in order to save performance by avoiding saving chunks that had no changes made to them.

As soon as the game generates a new chunk, that chunk is then immediately marked as “needs saving” by the game, causing the game to save those chunks the moment they get unloaded. This is very likely done to save performance by avoiding generating the same chunks every time a player comes in their range.

This mod overrides the rule above, and unflags newly generated chunks as “needs saving” anyways, causing them to not be saved once they get unloaded, unless a change is made to those chunks. This ends up shrinking the world size at the cost of performance, because the next time a player comes near those chunks, they will have to be generated again.

How well does the mod do?

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You can find that info on the GitHub page. The MinecraftPatch description formatting is not letting me properly place the code block here.

The trade-off

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Doing what the mod does has it’s own trade-offs, the main one being performance. By not saving newly generated chunks, they will have to be re-generated every time a player comes near them, or whenever the world is loaded once again. Generating chunks of course costs performance and takes time for the game to do, and the higher the render distance, the more performance it will cost.

It is because of this trade-off that the `UNFLAG_CHANCE` config property was introduced into the mod. This property defines the percentage of chunks that will be affected by the mod. By default, 100% of newly generated chunks are unflagged. Decrease this value to increase the world generation performance, but keep in mind that that will increase the world size as well.

Can the mod remove unused chunks generated before the mod was installed or while the mod was disabled?

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Edit: As of v1.2, it finally can, but it is very important that you read the important notice in the v1.2 changelog of the mod.

(For <v1.2) Unfortunately it can not. Any previously saved chunks will not be affected by the mod. Doing so would likely require the mod to mess with the world files by detecting and removing unused chunks from there, which I do not know how do to.

Configuring the mod

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There are several ways to configure the mod. The main way of configuring it is by going into the config directory and creating a nounusedchunks.properties file. To see the list of properties you can use, please visit the GitHub page. The MinecraftPatch description formatting doesn’t display code blocks properly.

Mod Menu and Cloth Config API
The easier way of configuring the mod is to install the Mod Menu and the Cloth Config API mods, and then use those mods to configure this mod in a settings menu while the game is running. Those mods are not required to run this mod.

A showcase of removing unused chunks

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This video shows how the mod can be used to remove “uninhabited” chunks to reduce world size (more info is in the v1.2 changelog).

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