[Python] `test_total_bytes_allocated` failing on CI

[h-vetinari]

Describe the bug, including details regarding any error messages, version, and platform.

In conda-forge/arrow-cpp-feedstock#1053, I currently have a failing test test_total_bytes_allocated on arrow 12 (though not arrow 11 or before), but some commit between arrow 12 and current main seems to have fixed this¹ - any ideas?

This is currently holding up all our migrations on the arrow-feedstock and is very high priority for us in conda-forge. Possible solutions:

• someone tells me that it's fine to skip that test
• we identify the relevant changes that regressed this from 11->12 and revert them (on the feedstock)
• we identify what fixed the issue between 12 & main and I backport those changes (on the feedstock)

Originally posted by @h-vetinari in #35637 (comment)

Component(s)

Packaging

Footnotes

1. as confirmed in GH-35658: [Packaging] Sync conda recipes with feedstocks #35637 ↩

[assignUser]

@westonpace is it fine to skip that test or do you know if that fix was already added for 12.0.1?

[h-vetinari]

Thanks @assignUser for chiming in! Some more context. It did not appear for the last successful build of 12.0.0, then appeared for a migration (of simultaneously re2, aws-crt & google-cloud-cpp; because reasons...), but only on linux, and not for any of the older arrow versions (which received the same migrator PRs).

Single test failure here, and only on linux. Normally I'd go with a skip, but this looks like it might be leaking memory? Any ideas? The test in question has no comments or documentation AFAICS.

=================================== FAILURES ===================================
__________________________ test_total_bytes_allocated __________________________

    def test_total_bytes_allocated():
>       assert pa.total_allocated_bytes() == 0
E       assert 1216 == 0
E        +  where 1216 = <built-in function total_allocated_bytes>()
E        +    where <built-in function total_allocated_bytes> = pa.total_allocated_bytes

It's also interesting that this doesn't appear in any of the equivalent PRs to the maintenance branches, e.g. #1057.

However, I've now restarted conda-forge/arrow-cpp-feedstock#1053, and although I have no idea why, the failure seems to have disappeared! 🥳

I'm happy to close this issue (and apologise for the noise), unless people want to leave this open a bit longer to understand better what's happening with test_total_bytes_allocated. As I mentioned above, it's hard to tell for me (from lack of code comments/context) what this test is actually testing, under which conditions it may fail, and how serious that is if it happens.

[jorisvandenbossche]

I think the context for that test is that in theory this method should always return zero if there is no data allocated/held by Arrow. And we are careful to ensure that in the tests we only create arrow data inside a test function (and for example not in the pytest.mark.parametrize values), to ensure that this assertion holds.

Now, why it would have temporarily failed, no idea.

[pitrou]

It might be that some data was held alive by the Python GC at this point, or perhaps some thread was lingering around? We should at least try to GC-collect at the start of the method.

[jorisvandenbossche]

This failure is not also happening on our own CI, for example the latest wheel-manylinux-2014-cp310-arm64 nightly build also has

 __________________________ test_total_bytes_allocated __________________________

    def test_total_bytes_allocated():
>       assert pa.total_allocated_bytes() == 0
E       assert 640 == 0
E        +  where 640 = <built-in function total_allocated_bytes>()
E        +    where <built-in function total_allocated_bytes> = pa.total_allocated_bytes

[pitrou]

Ok, perhaps we can simply execute this test in a subprocess to make it more reliable?