Requires CleanRoomMC https://cleanroommc.com/
Chunk Steward (initially uploaded as LazyChunks) is a 1.12.2 mod built to help with performance in world-gen heavy modpacks. This is built on Java 21 and will require CleanRoom MC to function. It will preload chunks around the player during idle time, and will throttle heavy chunk generation during exploration so that TPS issues are minimized. This can be very important in server environments so that exploring players don't completely freeze up server ticks. The result is somewhat slower chunk load in during exploration but more stable TPS overall.
Chunk Steward will also pregenerate a larger radius around areas the player has a spawn point or regularly occupies in anticipation of further exploration. It will do this only using idle CPU time to help prevent excessive server usage.
This also exposes an API that other mods can use to check for server utilization to better help minimize heavy server tick spikes during CPU intense generation. Two mods that are using this now are Roguelike Dungeons - Arcana Edition and Arcana Quest Tweaks.