`open_mfdataset` exits while sending a "Segmentation fault" error

[kasra-keshavarz]

What is your issue?

I try to open about ~10 files, each 5MB as a test case, using xarray's open_mfdataset method with the parallel=True option, however, it throws a "Segmentation fault" error as the following:

$ ipython
Python 3.10.2 (main, Feb  4 2022, 19:10:35) [GCC 9.3.0]
Type 'copyright', 'credits' or 'license' for more information
IPython 8.10.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: import xarray as xr

In [2]: ds = xr.open_mfdataset('./ab_models_198001*.nc', chunks={'time':10})

In [3]: ds
Out[3]: 
<xarray.Dataset>
Dimensions:              (time: 744, rlat: 140, rlon: 105)
Coordinates:
  * time                 (time) datetime64[ns] 1980-01-01T13:00:00 ... 1980-0...
    lon                  (rlat, rlon) float32 dask.array<chunksize=(140, 105), meta=np.ndarray>
    lat                  (rlat, rlon) float32 dask.array<chunksize=(140, 105), meta=np.ndarray>
  * rlon                 (rlon) float64 342.1 342.2 342.2 ... 351.2 351.3 351.4
  * rlat                 (rlat) float64 -7.83 -7.74 -7.65 ... 4.5 4.59 4.68
Data variables:
    rotated_pole         (time) int32 1 1 1 1 1 1 1 1 1 1 ... 1 1 1 1 1 1 1 1 1
    RDRS_v2.1_P_UVC_10m  (time, rlat, rlon) float32 dask.array<chunksize=(10, 140, 105), meta=np.ndarray>
    RDRS_v2.1_P_FI_SFC   (time, rlat, rlon) float32 dask.array<chunksize=(10, 140, 105), meta=np.ndarray>
    RDRS_v2.1_P_FB_SFC   (time, rlat, rlon) float32 dask.array<chunksize=(10, 140, 105), meta=np.ndarray>
    RDRS_v2.1_A_PR0_SFC  (time, rlat, rlon) float32 dask.array<chunksize=(10, 140, 105), meta=np.ndarray>
    RDRS_v2.1_P_P0_SFC   (time, rlat, rlon) float32 dask.array<chunksize=(10, 140, 105), meta=np.ndarray>
    RDRS_v2.1_P_TT_1.5m  (time, rlat, rlon) float32 dask.array<chunksize=(10, 140, 105), meta=np.ndarray>
    RDRS_v2.1_P_HU_1.5m  (time, rlat, rlon) float32 dask.array<chunksize=(10, 140, 105), meta=np.ndarray>
Attributes:
    CDI:          Climate Data Interface version 2.0.4 (https://mpimet.mpg.de...
    Conventions:  CF-1.6
    product:      RDRS_v2.1
    Remarks:      Variable names are following the convention <Product>_<Type...
    License:      These data are provided by the Canadian Surface Prediction ...
    history:      Mon Aug 28 13:44:02 2023: cdo -z zip -s -L -sellonlatbox,-1...
    NCO:          netCDF Operators version 5.0.6 (Homepage = http://nco.sf.ne...
    CDO:          Climate Data Operators version 2.0.4 (https://mpimet.mpg.de...

In [4]: type(ds)
Out[4]: xarray.core.dataset.Dataset

In [5]: ds = xr.open_mfdataset('./ab_models_198001*.nc', chunks={'time':10}, parallel=True)
[gra-login3:25527:0:6913] Caught signal 11 (Segmentation fault: address not mapped to object at address 0x8)
[gra-login3:25527] *** Process received signal ***
[gra-login3:25527] Signal: Segmentation fault (11)
[gra-login3:25527] Signal code:  (128)
[gra-login3:25527] Failing at address: (nil)
Segmentation fault

Here is the version of xarray:

In [5]: xr.show_versions()
/home/user/virtual-envs/scienv/lib/python3.10/site-packages/_distutils_hack/__init__.py:36: UserWarning: Setuptools is replacing distutils.
  warnings.warn("Setuptools is replacing distutils.")

INSTALLED VERSIONS
------------------
commit: None
python: 3.10.2 (main, Feb  4 2022, 19:10:35) [GCC 9.3.0]
python-bits: 64
OS: Linux
OS-release: 3.10.0-1160.88.1.el7.x86_64
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: en_CA.UTF-8
LOCALE: ('en_CA', 'UTF-8')
libhdf5: 1.12.1
libnetcdf: 4.9.0

xarray: 2023.7.0
pandas: 1.4.0
numpy: 1.21.2
scipy: 1.8.0
netCDF4: 1.6.4
pydap: None
h5netcdf: None
h5py: None
Nio: None
zarr: None
cftime: 1.6.2
nc_time_axis: None
PseudoNetCDF: None
iris: None
bottleneck: None
dask: 2023.8.0
distributed: 2023.8.0
matplotlib: 3.5.1
cartopy: None
seaborn: None
numbagg: None
fsspec: 2023.6.0
cupy: None
pint: None
sparse: None
flox: None
numpy_groupies: None
setuptools: 60.2.0
pip: 23.2.1
conda: None
pytest: 7.4.0
mypy: None
IPython: 8.10.0
sphinx: None

I'm working on an HPC, so if a list "modules" I have loaded helps, here it is:

$ module list

Currently Loaded Modules:
  1) CCconfig          5) gcccore/.9.3.0  (H)      9) libfabric/1.10.1      13) ipykernel/2023a           17) sqlite/3.38.5                   21) postgresql/12.4             (t)  25) gdal/3.5.1  (geo)  29) udunits/2.2.28 (t)    33) cdo/2.2.1             (geo)
  2) gentoo/2020 (S)   6) imkl/2020.1.217 (math)  10) openmpi/4.0.3    (m)  14) scipy-stack/2023a (math)  18) jasper/2.0.16            (vis)  22) freexl/1.0.5                (t)  26) geos/3.10.2 (geo)  30) libaec/1.0.6          34) mpi4py/3.1.3          (t)
  3) StdEnv/2020 (S)   7) gcc/9.3.0       (t)     11) libffi/3.3            15) hdf5/1.10.6       (io)    19) libgeotiff-proj901/1.7.1        23) librttopo-proj9/1.1.0            27) proj/9.0.1  (geo)  31) eccodes/2.25.0 (geo)  35) netcdf-fortran/4.5.2  (io)
  4) mii/1.1.2         8) ucx/1.8.0               12) python/3.10.2    (t)  16) netcdf/4.7.4      (io)    20) cfitsio/4.1.0            (vis)  24) libspatialite-proj901/5.0.1      28) expat/2.4.1 (t)    32) yaxt/0.9.0     (t)    36) libspatialindex/1.8.5 (phys)

  Where:
   S:     Module is Sticky, requires --force to unload or purge
   m:     MPI implementations / Implémentations MPI
   math:  Mathematical libraries / Bibliothèques mathématiques
   io:    Input/output software / Logiciel d'écriture/lecture
   t:     Tools for development / Outils de développement
   vis:   Visualisation software / Logiciels de visualisation
   geo:   Geography libraries/apps / Logiciels de géographie
   phys:  Physics libraries/apps / Logiciels de physique
   H:                Hidden Module

Thanks.

[welcome]

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[meteoDaniel]

Hey @kasra-keshavarz , I think your issue has to do with the fact that you are running parallel mode on a HPC. So it could be possible that the underlying dask.delayed is unable to utilize the hpc cores.

Can you check out dask.delayed on your machine ?

[keewis]

I think you're running into the issues described in #7079. You have two options for now: pin netcdf4<1.6.0 or don't use a threading scheduler (see the dask documentation on how to do that). It is truly unfortunate that we couldn't fix this up until now, but this is also very tricky to debug since it involves race conditions (which I can reliably reproduce locally, but ...)

[kasra-keshavarz]

Thank you both @meteoDaniel and @keewis, much appreciated.

I was wondering if the issue is related to Dask and it is causing this issue. Just a quick suggestions; I understand it is a completely separate issue from xarray and it is related to Dask, but since there is no meaningful error or warning being issue to the user, it was difficult for me to dig into the problem. If this could be mentioned in any of your documentations, it could be a great help to the next person facing the same issue. I close the issue here. Thank you again.