What does pre-generating chunks mean?Pre-generating chunks is a useful technique for servers to help reduce the server load in the future. In Minecraft, chunks generate as players walk around the world to new places. By pre-generating the chunks, your world will already be built and the server just has to load in the data rather than creating it. It is recommended to do this with only you online as it does cause major lag and resource usage whilst in progress but reduces the load afterwards.
What does trimming chunks mean?Trimming chunks means removing chunks that are outside of the specified world border [see below] so that the server uses less unnecessary storage. It doesn't remove any chunks you use, only ones outside of the specified zone set by you.
Requirements:Before pre-generating chunks, you need to make sure you have the following on your server:A form of Bukkit or Spigot (Forge and Vanilla servers will not work);
The latest version of WorldBorder (supports 1.8-1.12) which can be found here;
A decent server (for large pre-generating, 1-2GB servers may not be enough).
How do I pre-generate the chunks then?Install the WorldBorder plugin on your server and restart;
Stand in the centre of the world you wish to pre-generate (this is usually 0,0 but you may want to do it based off of where your server spawn is);
Type "/wb set <radius>" - this will make a square worldborder based on where you are standing. If you want a rectangle, use "/wb set <radiusX> <radiusZ>";
Make sure you are the only user online for the following steps as they will cause lag on your server. We recommend turning on whitelist with "/whitelist on";
Type "/wb fill" then "/wb fill confirm" to start the generation process. This will take a long time depending on the world size you chose.
You will receive regular updates from the plugin telling you exactly where it is in the process:
You will receive regular updates from the plugin:
__You can cancel the generation at any time with "/wb fill cancel", or pause it with "/wb fill pause".__OPTIONAL: Perform "/wb trim" to remove all generated chunks that are 13 chunks outside of your border. This will again take some time and should be performed with only you online.
Here are some images of what pre-generating and trimming your world look like.
These images are from Brettflan's WorldBorder plugin page on Bukkit:
