CI/BUG?: test_pct_max_many_rows crashes on travis-27.

[h-vetinari]

Following Ian Fleming ("Once is happenstance. Twice is coincidence. Three times is enemy action"), here are the three most recent builds from #23582 -- which only changes tests -- wherein there is a single failure/crash in the travis-27.yaml build for pandas/tests/series/test_rank.py::test_pct_max_many_rows, which looks like this:

[...]
........................................................................ [ 87%]
..........................................................[gw0] node down: Not properly terminated
fReplacing crashed worker gw0
gw2 [39907] / gw1 [39907]. [ 87%]
........................................................................ [ 87%]
........................................................................ [ 87%]
[...]
........................................................................ [ 99%]
.....
=================================== FAILURES ===================================
_______________________ pandas/tests/series/test_rank.py _______________________
[gw0] linux2 -- Python 2.7.15 /home/travis/miniconda3/envs/pandas/bin/python
Worker 'gw0' crashed while running 'pandas/tests/series/test_rank.py::test_pct_max_many_rows'

https://travis-ci.org/pandas-dev/pandas/jobs/455175414
https://travis-ci.org/pandas-dev/pandas/jobs/455259318
https://travis-ci.org/pandas-dev/pandas/jobs/455642129

Interestingly, the azure 2.7 builds pass both for windows and linux. Any ideas?

[jbrockmendel]

I’ve noticed this too. I’m guessing related to #23688. @jschendel any ideas?

[h-vetinari]

@jbrockmendel
Definitely something weird going on.

>>> import numpy as np
>>> import pandas as pd
>>> s = pd.Series(np.arange(2**24 + 1))
>>>
>>> s.astype(int).rank(pct=True).max()
1.0
>>> s.astype(np.int32).rank(pct=True).max()
1.0
>>> s.astype(np.int64).rank(pct=True).max()
1.0
>>> s.astype(np.uint32).rank(pct=True).max()
1.0
>>> s.astype(np.uint64).rank(pct=True).max()
1.0
>>> s.astype(float).rank(pct=True).max()
1.0
>>> s.astype(np.float64).rank(pct=True).max()
1.0
>>> s.astype(np.float32).rank(pct=True).max()
MemoryError
>>> # all following calls to s.astype(<whatever>).rank(pct=True), e.g.
>>> s.astype(int).rank(pct=True).max()
MemoryError
>>> # Interestingly, even after the MemoryError, pct=False works
>>> s.astype(int).rank().max()
16777217.0

I can't really see how anything in that test should cast to float32, but maybe there's a resource leak somewhere?

[TomAugspurger]

Is this crash 2.7 only, or have we seen it on python 3 builds?

[h-vetinari]

I've only ever seen it in the travis-27 build.

[TomAugspurger]

Unfortunately I haven't been able to reproduce the segfault locally on my Mac.

[h-vetinari]

I can reproduce the failure locally (on windows), but I only get a MemoryError, not a segfault. If it were a MemoryError, it could be an explanation why it only fails sometimes - depending on how busy the worker is with other code at that moment.