Memory leak in Sentry.withScope

[joulev]

Is there an existing issue for this?

• I have checked for existing issues https://github.com/getsentry/sentry-javascript/issues
• I have reviewed the documentation https://docs.sentry.io/
• I am using the latest SDK release https://github.com/getsentry/sentry-javascript/releases

How do you use Sentry?

Sentry Saas (sentry.io)

Which SDK are you using?

@sentry/node

SDK Version

10.25.0

Framework Version

No response

Link to Sentry event

No response

Reproduction Example/SDK Setup

import * as Sentry from "@sentry/node";
import v8 from "node:v8";

Sentry.init({ dsn: "<DSN HERE>" });

let count = 0;

function handle() {
  gc?.();

  const largeData = new Array(1000000).fill("hello");
  Sentry.withScope((scope) => {
    scope.setExtra("data", largeData);
    Sentry.captureMessage("hello");
  });

  const heapData = v8.getHeapStatistics();
  count++;
  if (count % 20 === 0) {
    console.log(`${heapData.total_heap_size}`);
  }
}

console.log(Sentry.SDK_VERSION);
while (true) {
  handle();
}

Steps to Reproduce

Run the above script with node --expose-gc.

$ node --expose-gc script.mjs

Expected Result

The logged value can fluctuate but should not go up.

Actual Result

10.25.0
213172224
373407744
533643264
693878784
854114304
1014349824
1174585344
1334820864
1495056384
1655291904
1815527424
1975762944
2136260608
2296496128
2456993792
2617491456
2777726976
2938224640
3098460160
3258957824
3419193344

<--- Last few GCs --->

[39532:0xb83400000]    66593 ms: Mark-Compact 3298.9 (3337.5) -> 3298.9 (3337.5) MB, pooled: 0 MB, 289.38 / 0.00 ms  (average mu = 0.006, current mu = 0.007) testing; GC in old space requested
[39532:0xb83400000]    67044 ms: Mark-Compact 3306.6 (3345.1) -> 3306.5 (3345.1) MB, pooled: 0 MB, 448.04 / 0.00 ms  (average mu = 0.006, current mu = 0.005) testing; GC in old space requested


<--- JS stacktrace --->

FATAL ERROR: Ineffective mark-compacts near heap limit Allocation failed - JavaScript heap out of memory
(and a bunch of other things)

Additional Context

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[linear]

JS-1168

[JPeer264]

Thanks for opening the issue and adding this nice reproduction. There is indeed some leak in here - we try to investigate how to mitigate the memory consumption

[joulev]

Actually now that I tried with async code, the leak is gone. I assume that in the reproduction above, due to the sync nature of the code, the GC didn't have enough time to collect everything.

All that is needed for the code above to no longer be leaky is just

await new Promise((resolve) => setTimeout(resolve, 0))

at the beginning of the handle() function.

What's interesting though is that in our production code, it is still leaky despite being async code. The below are the before and the after of removing withScope usage from the code

The production server does receive a lot of traffic, but I don't think it is so overloaded with traffic that the GC doesn't have a chance to run ever... I will try to make an async-based reproduction example.