Memory leak from gc metrics

[marwankhalili]

I work on a private monolith repository that is having issues with integration tests crashing due to memory leaks.

Managed to narrow down the memory leak to collectDefaultMetrics() in prom-client. Upon investigating the default metrics, I identified that gc was leaking memory. Example using jest --detectLeaks:

'use strict';

it('test gc metrics memory leak', () => {
    const gc = require('../../lib/metrics/gc');
    gc();
});

// > jest --detectLeaks
// FAIL

Looking at the gc metrics source code I noticed that a PerformanceObserver is created but disconnect() is never called (link to documentation).

I confirmed that calling disconnect() fixes the memory leak for our integration tests, as well as the example above.

Assuming we can't disconnect the observer, perhaps we could expose a stop() function that calls disconnect()? As proposed in PR #495 for eventLoopLag.

[timofriedlberlin]

Are there any plans when this is being addressed? We would really love to increase visibility to our applications but enabling this library basically grinds our application to halt.

[VictorZhang2014]

Me too. We use NestJs web framework and integrated the prom-client, the memory swelled up all the way as the prometheus monitor had requested the http://localhost:8080/metrics periodically.

Part of the error saying: Node Js: heap out of memory

It seems to be hard too solve the issue, I'm considering to use the golang library https://github.com/prometheus/prometheus

[jdmarshall]

Can we periodically clear the type=gc from Performace?

https://nodejs.org/api/perf_hooks.html#performanceobservertakerecords

[jdmarshall]

Where is the memory being collected at?

I'm looking at the perf code and I don't see any field accumulations. takeRecords() is pulling an empty list for node 24 and node 16.

Could this be something that behaved differently in older versions of node?

@marwankhalili what version of node were you testing with?

[jdmarshall]

I believe this has already been fixed by subsequent PRs.