Custom cacheHandlers for the new dynamicIO/PPR

[maral]

Summary

I am testing out dynamicIO and PPR and I wanted to see how it would behave if I ran it on multiple instances with a shared cache. Unfortunately, it seems most of the caching is now not being done using the old incremental cache handler (set by cacheHandler in next.config.ts), but rather using the new handlers that could be set up by experimental.cacheHandlers. This was quite difficult to find and even harder to use - there is no documentation yet and I couldn't make it work without breaking the build (it hangs until timeout of 60 seconds is depleted).

My questions are:

• Will it be possible to set up cross-instance caching in the new dynamicIO/ppr/cacheComponents?
• Is Next.js going to unify the old and the new cache handlers, so we don't need to keep multiple custom handlers in parallel?
• Is a thorough documentation planned for Next v16?
• What about pre-rendered static shells, such as those in /.next/server/app/index.html - could those be shared by multiple Node.js instances somehow (i.e., could there be an adapter to have a different storage instead of the filesystem)?

Example

I attach the repo branch I tested it out on, however it's not really that relevant.
https://github.com/maral/caching-experiments/tree/custom-cache-handlers

[Jordaneisenburger]

Hi @maral I'm trying to integrate https://github.com/fortedigital/nextjs-cache-handler which seems to work fine for Next.js 15+ even with some experimental features like cacheTag() and cacheLife() but unfortunately 'use cache' itself doesn't work yet.

When I set NEXT_PRIVATE_DEBUG_CACHE="1" in my .env file I can see the use cache writing to the default handler like so DefaultCacheHandler: set ["_RQNrbfs4s8k3Yb66CmIe","c0e05133f7a3e440bf585fdc82cedee9ca94980d5c",["jordan"]]

But unfortunately I have no clue how to get this into Redis instead of memory I'll keep investigating but if you have any pointers that would help a lot.

[maral]

Hi @Jordaneisenburger, thanks for the answer and I welcome the shared interest. I saw the same message using the debug mode, however I haven't succeeded with my attempts at using a custom handler there - you can check out the linked branch to see how I approached it. I think we need some examples / docs on how to do that properly and I believe the Next.js team will provide them as we approach v16.

[Jordaneisenburger]

Hi @maral,

I've checked and made a "dirty solution" as I'm unable to wait for the Next.js team to provide a simple solution to this issue. I figured that for the experimental 'use cache' directive it uses this file: node_modules/next/dist/server/lib/cache-handlers/default.external.js which uses memory cache by default. I changed it so it saves the cache to my Redis server and it seems to work.

So currently I can use the following experimental functionalities:

• 'use cache' (only tested inside functions, so not component or page level)
• cacheLife()
• cacheTag()

Invalidation also works in my POC environment, about to implement it in my real project.

For all the other non-experimental caching I use https://github.com/fortedigital/nextjs-cache-handler

I know you're testing PPR and dynamicIO but maybe this somehow helps, I can share the dirty fix if interested.

[maral]

Sure, even though I will most likely wait for the clean solution, I am interested :)

[magnusriga]

@Jordaneisenburger @maral :

I made a bug report with an MRE about this, today. In case useful, you can find it here: #82993