Issue reading parquet using pyarrow

[andersbogsnes]

When trying to read parquet files using Dask==2.15.0 and adlfs==0.3.0 I got exceptions that I didn't have before.

I boiled it down to the following example:
Using Azurite:

>>> import dask.dataframe as dd
>>> import pandas as pd
>>> from azure.storage.blob import BlobServiceClient
>>> conn_str = "DefaultEndpointsProtocol=http;AccountName=devstoreaccount1;AccountKey" \
         "=Eby8vdM02xNOcqFlqUwJPLlmEtlCDXJ1OUzFT50uSRZ6IFsuFq2UVErCz4I6tq/K1SZFPTOtr" \
           "/KBHBeksoGMGw==;BlobEndpoint=http://127.0.0.1:10000/devstoreaccount1;"
>>> client: BlobServiceClient = BlobServiceClient.from_connection_string(conn_str)
>>> client.create_container("test")
>>> df = pd.DataFrame(
    {
        "col1": [1, 2, 3, 4],
        "col2": [2, 4, 6, 8],
        "index_key": [1, 1, 2, 2],
        "partition_key": [1, 1, 2, 2],
    }
)
>>> STORAGE_OPTIONS = {"account_name": "devstoreaccount1", "connection_string": conn_str}
>>> dask_dataframe = dd.from_pandas(df, npartitions=1)
>>> dask_dataframe.to_parquet(
    "abfs://test/test_group",
    storage_options=STORAGE_OPTIONS,
    engine="pyarrow"
)
>>> data_out = dd.read_parquet("abfs://test/test_group",
                           engine="pyarrow",
                           storage_options=STORAGE_OPTIONS)
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/home/anders/.local/share/JetBrains/Toolbox/apps/PyCharm-P/ch-0/201.7223.92/plugins/python/helpers/pydev/_pydev_bundle/pydev_umd.py", line 197, in runfile
    pydev_imports.execfile(filename, global_vars, local_vars)  # execute the script
  File "/home/anders/.local/share/JetBrains/Toolbox/apps/PyCharm-P/ch-0/201.7223.92/plugins/python/helpers/pydev/_pydev_imps/_pydev_execfile.py", line 18, in execfile
    exec(compile(contents+"\n", file, 'exec'), glob, loc)
  File "/home/anders/.config/JetBrains/PyCharm2020.1/scratches/scratch.py", line 34, in <module>
    data_out = dd.read_parquet("abfs://test/test_group",
  File "/home/anders/.pyenv/versions/feature_env/lib/python3.8/site-packages/dask/dataframe/io/parquet/core.py", line 225, in read_parquet
    meta, statistics, parts = engine.read_metadata(
  File "/home/anders/.pyenv/versions/feature_env/lib/python3.8/site-packages/dask/dataframe/io/parquet/arrow.py", line 267, in read_metadata
    parts, dataset = _determine_dataset_parts(
  File "/home/anders/.pyenv/versions/feature_env/lib/python3.8/site-packages/dask/dataframe/io/parquet/arrow.py", line 198, in _determine_dataset_parts
    dataset = pq.ParquetDataset(paths, filesystem=fs, **dataset_kwargs)
  File "/home/anders/.pyenv/versions/feature_env/lib/python3.8/site-packages/pyarrow/parquet.py", line 1171, in __init__
    self.metadata_path) = _make_manifest(
  File "/home/anders/.pyenv/versions/feature_env/lib/python3.8/site-packages/pyarrow/parquet.py", line 1367, in _make_manifest
    raise OSError('Passed non-file path: {}'
OSError: Passed non-file path: test/test_group

Using fastparquet instead solves the problem - but last I tried, fastparquet didn't handle my filters properly, so I would prefer to be able to use pyarrow

[martindurant]

This exception seems to follow checks for fs.isdir(path) and fs.isfile(path). Do you have a chance to check whether the behaviour of those functions has changed for your path with the newer version of adlfs?
Given that the attempt to read immediately follows the write, can you try eliminating any caching effects by doing (I think)

import adlfs
adlfs.AzureDatalakeFileSystem.clear_instance_cache()

[andersbogsnes]

Sure!
Clearing cache had no effect - I assume you mean AzureBlobFileSystem, though neither has an effect.

I've had some issues with ls - continuing the snippet from above:

>>> fs = adlfs.AzureBlobFileSystem(**STORAGE_OPTIONS)
>>> fs.ls("test")
Traceback (most recent call last):
  File "/home/anders/.pyenv/versions/feature_env/lib/python3.8/site-packages/adlfs/core.py", line 518, in ls
    elif len(blobs) == 1 and blobs[0]["blob_type"] == "BlockBlob":
  File "/home/anders/.pyenv/versions/feature_env/lib/python3.8/site-packages/azure/storage/blob/_shared/models.py", line 191, in __getitem__
    return self.__dict__[key]
KeyError: 'blob_type'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/home/anders/.pyenv/versions/feature_env/lib/python3.8/site-packages/adlfs/core.py", line 534, in ls
    raise FileNotFoundError(f"File {path} does not exist!!")
FileNotFoundError: File  does not exist!!

But there is data in the container:

fs.ls("test/test_group")
['test/test_group/partition_key=1/', 'test/test_group/partition_key=2/', 'test/test_group/_common_metadata', 'test/test_group/_metadata', 'test/test_group/part.0.parquet']

Previous behaviour (just verified by rolling back)

>>> fs.ls("test")
['test/test_group/']

Interestingly, both fs.isdir and fs.isfile return False

>>> fs.isfile("test/test_group")
False
>>> fs.isdir("test/test_group")
False

Previous behaviour

>>> fs.isdir("test/test_group")
True
>>> fs.isfile("test/test_group")
False

Which probably is not good 😄

[hayesgb]

Do you observe this behavior with adlfs<0.3.0? The update to 0.3 migrates to Azure storage v12 from v2.0. It would be helpful to know if its related to this change.

[andersbogsnes]

@hayesgb You're fast 😄 Just updated my reply with equivalent behaviour from v0.2.4

[hayesgb]

LOL. I just sat down at my computer and saw this. I just added a branch "isfile_tests" that checks to verify if files and directories in the top level directory are identified properly. These pass, and can be found under test_core.py:

def test_isdir(storage):
    fs = adlfs.AzureBlobFileSystem(
        account_name=storage.account_name, connection_string=CONN_STR
    )
    assert fs.isdir("data") is True
    assert fs.isdir("data/root") is True
    assert fs.isdir("data/top_file.txt") is False


def test_isfile(storage):
    fs = adlfs.AzureBlobFileSystem(
        account_name=storage.account_name, connection_string=CONN_STR
    )
    assert fs.isfile("data") is False
    assert fs.isfile("data/root") is False
    assert fs.isfile("data/top_file.txt") is True

Two questions. 1) Any chance you can add a failing example, and 2) Can you share the versions of pyarrow, fastparquet, and fsspec you are using now vs what was working previously?

[andersbogsnes]

Sure - with a "pure" AzureBlobFileSystem (essentially copying your test) works fine - it seems the issue is with the way dask.dataframe.to_parquet writes the data when using the abfs backend.

So a complete failing example would be (again, using Azurite):

Versions:
adlfs=0.3.0
pandas = 1.0.3
azure-storage-blob=12.3.1
dask=2.16.0
fsspec=0.7.4
pyarrow=0.17.1
fastparquet=0.4.0

import dask.dataframe as dd
import pandas as pd
import adlfs
from azure.storage.blob import BlobServiceClient

conn_str = "DefaultEndpointsProtocol=http;AccountName=devstoreaccount1;AccountKey" \
           "=Eby8vdM02xNOcqFlqUwJPLlmEtlCDXJ1OUzFT50uSRZ6IFsuFq2UVErCz4I6tq/K1SZFPTOtr" \
           "/KBHBeksoGMGw==;BlobEndpoint=http://127.0.0.1:10000/devstoreaccount1;"

STORAGE_OPTIONS = {"account_name": "devstoreaccount1",
                   "connection_string": conn_str}

client: BlobServiceClient = BlobServiceClient.from_connection_string(conn_str)
container_client = client.create_container("test")

df = pd.DataFrame(
    {
        "col1": [1, 2, 3, 4],
        "col2": [2, 4, 6, 8],
        "index_key": [1, 1, 2, 2],
        "partition_key": [1, 1, 2, 2],
    }
)

dask_dataframe = dd.from_pandas(df, npartitions=1)

dask_dataframe.to_parquet(
    "abfs://test/test_group",
    storage_options=STORAGE_OPTIONS,
    engine="pyarrow",
)

fs = adlfs.AzureBlobFileSystem(**STORAGE_OPTIONS)
fs.ls("test")

Traceback (most recent call last):
  File "/home/anders/.pyenv/versions/feature_env/lib/python3.8/site-packages/adlfs/core.py", line 518, in ls
    elif len(blobs) == 1 and blobs[0]["blob_type"] == "BlockBlob":
  File "/home/anders/.pyenv/versions/feature_env/lib/python3.8/site-packages/azure/storage/blob/_shared/models.py", line 191, in __getitem__
    return self.__dict__[key]
KeyError: 'blob_type'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/home/anders/.pyenv/versions/feature_env/lib/python3.8/site-packages/adlfs/core.py", line 534, in ls
    raise FileNotFoundError(f"File {path} does not exist!!")
FileNotFoundError: File  does not exist!!

Should this be a Dask issue instead? Seems like to_parquet is writing files in an unexpected manner, which causes errors when trying to read them again.

[martindurant]

Can you tell whether files have indeed been created in the blob container?

[andersbogsnes]

Yes, I can do the following:

>>> fs.ls("test/test_group")
['test/test_group/_common_metadata', 'test/test_group/_metadata', 'test/test_group/part.0.parquet']

I have also "manually" confirmed by checking with the BlobStoreClient directly

[martindurant]

If ls("test/test_group") works, but ls("test") does not, because it apparently tries to list the root/empty path, then the problem does lie here. Why dask should need to list the parent directory is another matter.

[andersbogsnes]

I think the issue arises, because dask is trying to do fs.isdir("test/test_group") which returns False, which is new behaviour.

Digging into the adlfs/fsspec code, this is probably because fs.info("test/test_group") also raises the same error as fs.ls("test") which makes sense, since fs.info delegating to AbstractFileSystem, which calls ls: https://github.com/intake/filesystem_spec/blob/master/fsspec/spec.py#L538

What I don't understand is why ls is getting screwed up by dask writing a parquet file to it...

[andersbogsnes]

Sorry to resurrect, but just wanted to know if this example was reproducible or if I'm the only one having the problem?

[hayesgb]

I'm looking into it.

[hayesgb]

I believe I have a fix for this. In some instances, Azure Blob Filesystem will return an ItemPaged iterator instead of a BlobPrefix. The scenario you were seeing appears to be one of those instances, so it wasn't being picked up. I'm going to do a push to master. Any chance you can take a look and see if it fixes your issue?

[andersbogsnes]

@hayesgb That's great news! My test case is working fine now, looks like you found the issue 👍

[hayesgb]

Sounds great. I've released this in 0.3.1.