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Increased memory usage in nodejs version 20.16.0 due to fetch() #54274
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FWIW @snyamathi believes that this is caused by nodejs/undici@63b7794
CC @nodejs/undici
Possible fix in nodejs/undici#3445
First, a memory leak happens when the memory is never released. In the diagram above, the gc is at work in claiming/releasing all the memory. Therefore, this bug is not a memory leak, but a less panicking "increased memory usage" bug.
Second, I would really love to see a reproduction that is not using Next.js, because it monkey-patches fetch()... which might interact badly with the "fire and forget" logic of undici (we need to support fetches that do not consume the request).
- changed the title
[-]Memory Leak in nodejs version 20.16.0[/-][+]Increased memory usage in nodejs version 20.16.0 due to fetch()[/+]on Aug 9, 2024 I've done a bit of research on this problem, and I came to these conclusions:
- Next.js monkey patches global
fetch()in https://github.com/vercel/next.js/blob/9a1cd356dbafbfcf23d1b9ec05f772f766d05580/packages/next/src/server/lib/patch-fetch.ts#L786-L796. - Using vanilla undici in the provided example does not show the problem, this is also highlighted in Possible memory leak in Fetch API vercel/next.js#68636 (reply in thread).
- fix: increased memory in finalization first appearing in v6.16.0 undici#3445 improves memory consumption by roughly 10% in my tests without visible issues. I couldn't replicate whether it fixes the problem, but I'll ship a release with this anyway, as it's a good improvement. I don't expect it to fix the problem.
Something in the latest undici releases increased memory consumption for the Next.js cache. This does not affect vanilla
fetch()users.We need a reproduction without Next.js or
React.cache()that clearly shows the problem. I couldn't isolate it myself, and I've exhausted the time I could dedicate so far.I've been trying to follow what their patching does, but I were not able to identify the problem.
Reacted by Long TranReacted by khuezy, Jasper Meijaard, 정대윤(daeyunjeong), Alcodeos and R1- Next.js monkey patches global
#54286 contains the patched version of undici.
That PR has landed, so I've closed this issue. Feel free to reopen if you disagree.
I am encountering this with an Express app (not Next.js) and it appears to be an actual leak in my case. The heap grows until the process crashes with
FATAL ERROR: Ineffective mark-compacts near heap limit Allocation failed - JavaScript heap out of memory. It crashes eventually even with--max-old-space-size=1000, while on Node 20.15.1, it remains stable permanently with--max-old-space-size=50.I'll try distilling to a minimal repro case, it sounds like that could still be useful? Or are we likely all set with that PR?
Open a new issue, this case is very specific to Next.js, so it'll likely be something else.
Reacted by RandallWe encountered this bug and confirmed that it still exists in 20.17.
If you run into this issue, please use 20.15.1 temporarily. Upgrading to latest nodejs v22 might also help@kouhin the fix landed in undici v6.19.6 and Node 20.17 still uses undici v6.19.2
nodejs/undici@v6.19.5...v6.19.6
https://github.com/nodejs/node/blob/v20.17.0/src/undici_version.h#L5
edit: I've opened a PR to backport the fix to Node v20 #54583
Reacted by Kou, Yves Amsellem and Lucas2 remaining items
reopening to track until this ships in v20.
Reacted by Kou, Patrick Piwowarczyk, Pepijn, Steven and Alexander KachkaevAfter reverting to 20.15.1 we now have a more stable memory utilisation (AWS ECS Fargate):
@mcollina we are on v20, is there a suggested workaround rather than going to v22 or waiting for the next release or do we downgrade to 20.15.1 and use
--max-old-space-size?You can always download the latest
undicifromnpmand use that?@redyetidev we tried that however it didn’t work for us
You may be experiencing a different issue, if so, please open in issue in nodejs/help or nodejs/undici
This is getting off topic for this issue, but the global fetch (https://nodejs.org/dist/latest-v20.x/docs/api/globals.html#fetch) which comes with node itself is different than adding a dependency on the npm package
undiciIn theory, you could patch the global fetch with the npm package, though in practice you're probably better off just sticking to a version before this issue was present (eg 20.15.1) or after the patch is backported (TBD).
The reason you don't want to patch
fetchis because (assuming you're using it) both Next.JS AND React separately patch the globalfetchfunction which may cause issues if done out of order. You could get around this by preloading the patch at startup, but why complicate things. Just downgrade or wait 😄Reacted by Tim PhilipsAdding up, had to downgrade to 20.15.1 to fix the leak on my project with Next.js (v14.2.5 - this didn't change).
Will probably stick to node 20.15.1 as 20.17 LTS causes the leak.@redyetidev downloading undici would do the trick at the cost of having yet another dependency (and we should remind to remove it sooner or later when we'll upgrade node).
Any ETA on this get back port to v20?
Reacted by Brian Mortenson, Tan Zi Gang, David Johansson, Ade Novid and Tim NovisI have the same problem with Next.js and Node v20.16 and v20.17
- linked a pull request that will close this issuev20.18.0 release proposal #55170
on Oct 3, 2024 The fix shipped in Node.js v20.18.0
Reacted by Sebastian Österberg, Brian Mortenson, Harry Scheuerle, Mustafa Hamza, Fonger, Mert Can Altin, Aashutosh Rathi and Nicolas ToffoloReacted by Toni Villena, Julian Yerfino, Trivikram Kamat, Steven, Lorenzo Stramaccia, Tan Zi Gang, Lucas, takayuki hara, Harry Scheuerle, Mustafa Hamza and 4 moreDoes anyone know if this also affected node v20.11.1? We're seeing a potential memory leak in next v14.2.7 with the pages router, but it's not as obvious with next v13.5.6, so I'm struggling to find the real issue.
- added a commit that references this issue
on Mar 6, 2025
Discussed in https://github.com/orgs/nodejs/discussions/54248
Originally posted by SteffenHo August 7, 2024
We saw a massive increase in memory in our next.js application after updating to version 20.16.0. We build our application with docker and the 20-alpine image. Other users were also able to confirm this problem: https://www.reddit.com/r/node/comments/1ejzn64/sudden_inexplicable_memory_leak_on_new_builds/
We then switched to version 20.15.1 and the memory returned to normal.
Maybe someone else could confirm this problem too?
@ronag could you have a look into this?