Cache behavior in WebGL

In Unity WebGL, the Cache API lets you store the asset data cached in .data files and AssetBundles within the browser cache. Storage limits for the browser cache such as maximum file size, maximum overall cache size, and eviction criteria are dependent on the browser and platform that you’re using. For more information, see Browser storage limits and eviction criteria.

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To access Data Caching, open the Publishing Setings for WebGL from File > Build Settings > Player Settings. This enables the browser to cache the main data files into the IndexedDB database.

Using the default browser HTTP cache doesn’t guarantee that the browser caches a particular response. This is because the browser HTTP cache has limited space, and the browser might not be able to cache files that are too large.

To improve your loading speed, IndexedDB allows you to cache files above the browser limit. When you cache more files, you increase the chance that downloaded content is available on the user’s machine during the next run of the build.

Data Caching only caches the .data files in the IndexedDB cache for HTTP responses. To cache AssetBundles, you need to enable Data Caching and override unityInstance.Module.cacheControl(). To do this, make sure Module.cacheControl(url) returns must-revalidate for the requested AssetBundle URL. For example, you can override the unityInstance.Module.cacheControl() function in the fulfillment callback of the Promise that createUnityInstance() returns. For further information on createUnityInstance(), see Compressed builds and server configuration.

Customize the WebGL Cache behavior

By default, the WebGL Cache stores the asset data file .data and AssetBundle files .bundle, and revalidates them before loading them from the cache. You can change this behavior by adding a new WebGL Template that changes the UnityLoader configuration.

The following example shows adding a custom cacheControl function to the UnityLoader configuration within the index.html file.

var config = {
   // ...
#if USE_DATA_CACHING
   cacheControl: function (url) {
     // Caching enabled for .data and .bundle files.
     // Revalidate if file is up to date before loading from cache
     if (url.match(/\.data/) || url.match(/\.bundle/)) {
         return "must-revalidate";
     }

     // Caching enabled for .mp4 and .custom files
     // Load file from cache without revalidation.
     if (url.match(/\.mp4/) || url.match(/\.custom/)) {
         return "immutable";
     }

     // Disable explicit caching for all other files.
     // Note: the default browser cache may cache them anyway.
     return "no-store";
   },
#endif
   // ...
}

The cacheControl function takes the url of a request as a parameter and returns one of the following:

• must-revalidate - If the function returns must-revalidate, the cache returns to an enabled state and the file is revalidated before being loaded from the cache.

• immutable - If the function returns immutable, the cache is enabled and the file is loaded from the cache without revalidation.

• no-store - If the function returns no-store, the cache is disabled.

The browser automatically stores (caches) certain file types such as .html, .js, .css, .json, .jpg, .png, so they don’t need to be explicitly stored in the WebGL Cache. Typical candidates for the WebGL cache include large files and files that use a custom file format.