gctime memory issue question

[hovelopin]

I encountered a memory issue in my Next.js project, and the cause was the gcTime configuration.

When I removed the existing 24-hour gcTime setting or changed it to 0, the memory leak was resolved, but I don't understand why.
From what I know, gcTime is set to Infinity by default in Next.js server environments, so it seems like memory wouldn't be released and should cause problems, but that wasn't the case. What could be the issue here?

For testing, I repeatedly sent curl requests to the suspected page and confirmed JS OOM errors. After removing code piece by piece to track down the cause, I was able to resolve the issue by changing the gcTime setting value.

[TkDodo]

looks like the queryClient is created outside of the component / request scope and thus sticks around

[hovelopin]

@TkDodo

Thank you for your response.
However, I didn't understand it perfectly, so could you review the project below and give me some advice?
The testing method was conducted as follows:

npm run build
npm run start:memory-test
for i in {1..500}; do curl http://localhost:3000/ko; done

When the gcTime of the useUsers hook is 0, no error occurs, but when it's not 0, a JS OOM issue occurs.

project : https://github.com/hovelopin/gctime-oom

[hovelopin]

After checking, it seems the problem only occurs when used together with the next-intl library.

[4l3ss]

Hi, we had a similar issue, where the queryClient had gcTime: Infinity, and some queries were prefetched server side.

Then some other query - only loaded client side with useQuery - further down in the component tree had a gcTime set to 24h.
This made the whole queryClient not gargbage collectable by nodejs because of a dependency looking like :

timers -> query with set gcTime -> queryclient -> [all other queries prefetched with default Infinity gcTime].

The queryClient is created with cache() so that it is unique per request.
Without that one query with the changed gcTime, the whole queryClient and queries were then properly garbage collected by nodejs after the nextjs request was done processing.

The fix was to either

• remove the gcTime of that client side query, so that it uses the default from the client (ie: Infinity on server, 5 minutes on client)
• or replace it with a ternary such as isServer ? Infinity : 24*60*60*1000

Maybe unrelated, but sharing because we spent quite some time digging into the heap dumps trying to understand what was happening.

[4l3ss]

@TkDodo I guess this would be an expected behaviour ?
Maybe something could be written in that section : https://tanstack.com/query/latest/docs/framework/react/guides/ssr#high-memory-consumption-on-server
Warning that, even though queryClient gcTime is Infinity, any queries redefining gcTime would make the actual garbage collection by nodejs for queries with default gcTime happen only after those additional queries with custom gcTime timers are gone.