Fast Advancements

Fast Advancements is a lightweight performance mod for Minecraft 1.12.2, designed to eliminate tick stuttering and CPU lag spikes caused by vanilla processing of achievements and inventory, especially in heavy modpacks with thousands of advancements

How It Works

Minecraft’s default system constantly scans the player’s inventory and evaluates kill triggers against each achievement JSON file loaded upon world entry, during combat, and when objects are moved. When there are hundreds or thousands of achievements loaded, this causes severe CPU thread blocks and RAM saturation

Fast Advancements replaces this unoptimized iteration logic with a surgical, multi-layered approach:

• Warm-up Delay: Temporarily defers heavy achievement checks during the initial ticks upon entering the world or server, preventing stuttering and freezes upon spawning
• Single-pass inventory counting: Scans inventory slots only once using fast primitive counters (fullStacks, emptySlots, occupiedSlots) instead of allocating redundant objects on every check
• Early Exit on Kill Triggers (Early-Exit Kill Triggers): Instantly skips the evaluation of damage sources not originating from the player and invalid target entities before iterating through the achievement list
• Tick Skipping: Limits the frequency of repetitive inventory checks during rapid object movement (shift-click, auto-crafting) to save CPU cycles without altering progress logic

Note: Fast Advancements does not alter game mechanics or disable achievements, it simply optimizes how and when the criteria are evaluated internally. Basically, it stabilizes the world upon loading

Performance Testing

In test environments with heavy modpacks loading between 2,000 and over 4,000 achievements:

• Stability upon entering the world: Eliminates initial FPS drops and “Server thread/WARN - Can't keep up!” messages immediately after spawning
• Reduced combat stuttering: Prevents micro-stuttering (Garbage Collection lag) when killing mobs or clearing entity farms
• Inventory efficiency: Smooths out frame drops when moving large quantities of items with Shift-click into chests or storage nets

The impact on performance varies depending on the total number of achievements loaded, the single-core processing power of the CPU, and the size of the modpack

Note: It does not improve overall performance, but it does slightly improve world loading by stabilizing it faster and indirectly helps the CPU and hard drive when loading the world

License and Source Code

This project is licensed under the GNU General Public License v3.0 (GPLv3). It is open source and completely free to include in any modpack

Reporting Bugs

If you encounter any issues, please report them in the GitHub Issue Tracker