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

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

     [ https://issues.apache.org/jira/browse/ARROW-11400?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Joris Van den Bossche resolved ARROW-11400.
-------------------------------------------
    Fix Version/s: 3.0.0
       Resolution: Fixed

Issue resolved by pull request 9350
[https://github.com/apache/arrow/pull/9350]

> [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
>            Priority: Minor
>              Labels: dataset, pull-request-available
>             Fix For: 3.0.0
>
>          Time Spent: 40m
>  Remaining Estimate: 0h
>
> 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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