How to Reset Chunks in Minecraft (Reduce File Size & Lag)

You explored 10,000 blocks in one direction looking for a Mangrove Swamp. You didn't find one. Now your save file is 5GB. Your server is lagging like it's running on a toaster. Backup takes an hour.

You need to trim the fat. You need to Reset Chunks.

What does "Resetting Chunks" actually do?

It deletes the parts of the world you explored but didn't build in. When you go back there, Minecraft will regenerate them as if they were new. This is how you get new biomes in old worlds without starting over. WARNING: If you delete a chunk with your base in it, say goodbye. It is gone. BACK UP YOUR WORLD. Do it now. I am not responsible if you delete your dog.

The Tool: MCA Selector

Do not try to do this manually. Use MCA Selector. It is a free tool that shows you a map of your world save.

Step 1: Open Your World

1. Close Minecraft.
2. Open MCA Selector.
3. File -> Open World. Navigate to the region folder in your save.

Step 2: The "Inhabited Time" Trick

How do you know which chunks are junk? You use a filter: InhabitedTime. This value tracks how long players have spent in a chunk.

• High Value: Your base (You spent hours there).
• Low Value: Random terrain you flew over once.

Go to Tools -> Filter Chunks. Set mode to "Selection". Condition: InhabitedTime < 5 minutes (or 6000 ticks). This will automatically select 90% of the useless chunks you generated while elytra flying.

Step 3: Visual Check

Look at the map. Are there any big orange squares selected? Zoom in. Is that your gold farm? Unselect it. Be careful. The tool doesn't know you love that dirt hut.

Step 4: Delete

1. Selection -> Delete Selected Chunks.
2. Close the tool.
3. Open Minecraft.

Why do this?

1. File Size: I once shrank a 20GB server map to 2GB.
2. New Updates: If the next update adds a new biome, you can delete old terrain near your base, and the new biome might spawn there.

Clean your room. Clean your world.