This override is used by the cache adapter (opens in a new tab) that is provided by OpenNext to the NextServer. It is also used by OpenNext if enableCacheInterception is set to true in the configuration.

It is used for retrieving and updating the ISR/SSG cache as well as the fetch cache used by Next.js. It does not handle anything related to cache tags (i.e. revalidateTag and revalidatePath)

If you want to better understand how to implement your own IncrementalCache, the easiest way would be to take a look at the existing included IncrementalCache (opens in a new tab).

One thing to note is that it is not used at build time, only at runtime. This means that you'll have to upload the cache yourself if you want to use the prebuilt routes/pages (And this is mandatory for ISR/SSG routes with fallback:false). All the cache files are present in the .open-next/cache folder. The one under BUILD_ID are for the ISR/SSG cache and the one under __fetch/BUILD_ID are for the fetch cache.