FastAssetBundleLoader

Game loads faster with large size mods by caching asset bundles.

It speeds up repeated mod startup by caching slow asset bundles into reusable files in a shared folder under Valheim's Unity persistent data path. The implementation is based on the same general approach as DiFFoZ's BepInExFasterLoadAssetBundles, but is adapted and trimmed for this Valheim-focused project. https://thunderstore.io/c/lethal-company/p/DiFFoZ/BepInEx_Faster_Load_AssetBundles_Patcher/

What it does

• It caches Valheim mod asset bundles that are stored in LZ4HC format into reusable LZ4 cache files, so subsequent loads can be faster.
• This is patcher.dll so it needs to be placed in BepInEx/patchers folder

Cache behavior

• Cache files are stored under <Application.persistentDataPath>/FastAssetBundleLoader/cache/v1 by default. On Windows this is normally %USERPROFILE%/AppData/LocalLow/IronGate/Valheim/FastAssetBundleLoader/cache/v1.
• Profiles using the same storage root reuse cache entries for identical bundle contents. Changed bundles get separate entries. v1 is the cache format version, not the mod release version.
• In BepInEx/config/sighsorry.fast_asset_bundle_loader.cfg, leave [General] CacheRootDirectory empty for the default location, or set an absolute storage root on another drive. FastAssetBundleLoader/cache/v1 is always appended. Relative paths are not accepted.
• Old CacheDirectory settings and caches under BepInEx/cache are not used or migrated. Existing files are left untouched; the shared cache is populated as eligible bundles load.
• Only one game process can use a given cache directory at a time. If the cache is busy or inaccessible, the other instance uses original bundle loading without caching for that run. An existing .cache.lock file is normal; the open file handle, not the file's presence, determines ownership.
• To reset the shared cache, close all game instances and delete only the dedicated FastAssetBundleLoader/cache/v1 directory. Do not delete the Valheim save-data directory. Resetting the cache affects every profile sharing that location.
• Cache files are created only when eligible asset bundles are actually loaded.
• A single run may not warm every cache entry if the game is closed before the background queue finishes or if some bundles are loaded only in specific scenes. Later runs may therefore become faster.
• For a broader warm-up, enter a world instead of stopping at the lobby and keep the game running until cache activity settles. Different gameplay paths may create additional entries, so caching every installed asset bundle is not guaranteed.
• Cache could take up to few GB of your disk space according to the mods you are using. (More than 3GB in my case)
• The main measured benefit is repeated loading to the lobby. Improvements from lobby to world depend on which eligible bundles are loaded and may not be noticeable in every setup.

Other mods to run the game faster

• StartupAccelerator
• LocalizationCache

I have tested with following combination to measure loading time.

• Modpack only = 246s
• FastAssetBundleLoader + Modpack = 170s
• StartupAccelerator + Modpack = 202s
• LocalizationCache + Modpack = 218s
• FastAssetBundleLoader + LocalizationCache + Modpack = 145s
• FastAssetBundleLoader + StartupAccelerator + Modpack = 127s

StartupAccelerator is faster but some mods might not work properly with it.