[jira] [Created] (ARROW-11400) [Python] Pickled ParquetFileFragment has invalid partition_expresion with dictionary type in pyarrow 2.0

["Joris Van den Bossche (Jira)" <ji...@apache.org>]

Joris Van den Bossche created ARROW-11400:
---------------------------------------------

             Summary: [Python] Pickled ParquetFileFragment has invalid partition_expresion with dictionary type in pyarrow 2.0
                 Key: ARROW-11400
                 URL: https://issues.apache.org/jira/browse/ARROW-11400
             Project: Apache Arrow
          Issue Type: Bug
          Components: Python
            Reporter: Joris Van den Bossche
            Assignee: Joris Van den Bossche


From https://github.com/dask/dask/pull/7066#issuecomment-767156623

Simplified reproducer:

{code:python}
import pyarrow.parquet as pq
import pyarrow.dataset as ds

table = pa.table({'part': ['A', 'B']*5, 'col': range(10)})
pq.write_to_dataset(table, "test_partitioned_parquet", partition_cols=["part"])

# with partitioning_kwargs = {} there is no error
partitioning_kwargs = {"max_partition_dictionary_size": -1}
dataset = ds.dataset(
    "test_partitioned_parquet/", format="parquet", 
    partitioning=ds.HivePartitioning.discover( **partitioning_kwargs)
)

frag = list(dataset.get_fragments())[0]
{code}

Querying this fragment works fine, but after serialization/deserialization with pickle, it gives errors (and with the original data example I actually got a segfault as well):

{code}
In [16]: import pickle

In [17]: frag2 = pickle.loads(pickle.dumps(frag))

In [19]: frag2.partition_expression
...
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xf1 in position 16: invalid continuation byte

In [20]: frag2.to_table(schema=schema, columns=columns)
Out[20]: 
pyarrow.Table
col: int64
part: dictionary<values=string, indices=int32, ordered=0>

In [21]: frag2.to_table(schema=schema, columns=columns).to_pandas()
...
~/miniconda3/envs/arrow-20/lib/python3.8/site-packages/pyarrow/table.pxi in pyarrow.lib.table_to_blocks()

ArrowException: Unknown error: Wrapping ɻ� failed
{code}

It seems the issue was specifically with a partition expression with dictionary type. 
Also when using an integer columns as the partition column, you get wrong values (but silently in this case):

{code:python}
In [42]: frag.partition_expression
Out[42]: 
<pyarrow.dataset.Expression (part == [
  1,
  2
][0]:dictionary<values=int32, indices=int32, ordered=0>)>

In [43]: frag2.partition_expression
Out[43]: 
<pyarrow.dataset.Expression (part == [
  170145232,
  32754
][0]:dictionary<values=int32, indices=int32, ordered=0>)>
{code}

Now, it seems this is fixed in master. But since I don't remember it was fixed intentionally ([~bkietz]?), it would be good to add some tests for it.



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