Decompressinator

NMS-Decompressinator

NMS-Decompressinator is a batch script by CheatFreak that uses PSARC and NMSResign to automatically process the game ".pak" files by unpacking them and repacking with compression disabled to improve game performance by eliminating CPU spikes caused by on-the-fly ".pak" decompression without running the game fully unpacked, which introduces longer loading times due to the file system strain caused by the game needing to open handles to thousands of files.

The amount of improvement this has on performance is variable from PC to PC, but it should make a small difference even on high end machines. If nothing else, it addresses that commonly experienced lag spike when leaving the atmosphere of a planet, and other similar smaller lag spikes that occur during gameplay situations where data is loading, and should generally improve the loading times when loading into a save file, warping from system to system, or using teleporters.

Instructions & Download

1. Download NMS-Decompressinator from GitHub.
2. Extract the 7z file.
3. Move/Copy "NMS-Decompressinator.bat", "psarc.exe", and "NMSResign.exe" to your install folder in "GAMEDATA\PCBANKS".
4. Ensure you have at least 40GB of free space on the disk your install of No Man's Sky is on.
5. Run "NMS-Decompressinator.bat".
6. Wait patiently. This takes quite a while to run. You will see a completion message when it is done.
7. Test the game and make sure it works.
8. (Optional) Delete the backup of the original packed files by deleting the new "PackedFileBackup" folder to save space.

After running this tool, in the event that No Man's Sky on Steam updates, the game files will no longer be "validated" and it will result in getting a tamper warning on boot. If this happens, the game will likely still function fine, but you should probably validate the game cache on Steam, delete the old "PackedFileBackup" folder if it exists, and run Decompressinator again to ensure any new or updated ".pak" files are fully uncompressed.

Full Technical Explanation

No Man's Sky uses a format called PSARC (PlayStation Archive) for compressing it's files, with the file extension ".pak". These ".pak" files are located in the subfolder of the install of the game "GAMEDATA\PCBANKS".

These files, like the name suggests are archives that store game files with compression and are decompressed on the fly by the game as needed. Externally, they can decompressed using various tools, including PsArcTool, or the PlayStation SDK tool PSARC. Even while in game the decompression requires a small amount of work to perform for the CPU and thus, during loading sequences and cases where the game must draw data out of these ".pak" files, the game will try to decompress this data as quickly as possible so it can immediately load it into memory.

This process causes CPU usage spiking, and when CPU usage spikes, it can draw CPU cycles away from other operations on the computer, as well as the rest of the game's tasks, resulting in lag spikes. As mentioned above, the most common example of this in No Man's Sky is when you exit the atmosphere of a planet. The game needs to load in meshes for many space objects, including the Space Anomaly and Space Stations, and this data is drawn out of "NMSARC.MeshMisc.pak", and when it does so, it causes an obvious lag spike. All methods for fixing this involve the same sort of solution. Unpacking the file responsible for the spike, and either running it unpacked directly, or repacking the offending files with compression disabled.

Now, it's possible to run No Man's Sky with completely decompressed, unpacked files by unpacking these archives and moving the data out of PCBANKS and into the raw GAMEDATA folder, but this presents a different unique problem. Unpacked, the game no longer has problems with getting the files quickly, but instead, is beholden to being limited by disk file system access. No Man's Sky typically avoids this because most of the data is loaded out of only a handful of files (76 ".pak" files at the time of writing). So it opens one handle to a single file, decompresses and immediately has in memory all of the files it needed from that ".pak".

When you decompress and unpack the game files, rather than accessing only a few individual files, it has to access thousands of files. This is more a consequence of how modern PC file systems work than anything. One example to illustrate the cause is how when you copy a large amount of small files from one disk to another, the graph Windows displays spikes up and down with each tiny file and your overall transfer rate is worse with hundreds of tiny files that take up little space than when transfering fewer larger files between the same two disks. This is because the transfer rate drops when it has to update the file system with the new data, it is waiting on the file system to continue. The problem is similar here with file reads but on a smaller scale. The end result of running the game fully unpacked is that you get fewer lag spikes thanks to not needing decompression, but your overall loading times suffer compared to loading from ".pak" files because of the strain on the file system. The more files the game needs to load, the worse loading times will be.

Fortunately there is a solution. It is possible to repack the game files into archives that have data compression disabled entirely. PSARC (the PlayStation SDK tool) can be used to create ".pak" files that have compression disabled, resulting in ".pak" files that do not require any work to decompress on the fly by the game. Decompressinator automates the decompression and repacking of ".pak" files inside the "GAMEDATA\PCBANKS" folder, and it also updates the "BankSigniture.bin" file to match the new decompressed ".pak" files using NMSResign to prevent the game from complaining about the files being tampered with.