Benoit Rostykus created ARROW-6844:
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Summary: List<scalar type> columns read broken with 0.15.0
Key: ARROW-6844
URL: https://issues.apache.org/jira/browse/ARROW-6844
Project: Apache Arrow
Issue Type: Bug
Components: C++, Python
Affects Versions: 0.15.0
Reporter: Benoit Rostykus
Columns of type `array<primitive type>` (such as `array<int32>`,
`array<int64>`...) are not readable anymore using `pyarrow == 0.15.0` (but were
with `pyarrow == 0.14.1`) when the original writer of the parquet file is
`parquet-mr 1.9.1`.
```
import pyarrow.parquet as pq
pf = pq.ParquetFile('sample.gz.parquet')
print(pf.read(columns=['profile_ids']))
```
with 0.14.1:
```
pyarrow.Table
profile_ids: list<element: int64>
child 0, element: int64
...
```
with 0.15.0:
```
Traceback (most recent call last):
File "<string>", line 1, in <module>
File
"/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/pyarrow/parquet.py",
line 253, in read
use_threads=use_threads)
File "pyarrow/_parquet.pyx", line 1131, in
pyarrow._parquet.ParquetReader.read_all
File "pyarrow/error.pxi", line 78, in pyarrow.lib.check_status
pyarrow.lib.ArrowInvalid: Column data for field 0 with type list<item: int64>
is inconsistent with schema list<element: int64>
```
I've tested parquet files coming from multiple tables (with various schemas)
created with `parquet-mr`, couldn't read any `array<primitive type>` column
anymore.
I _think_ the bug was introduced with [this
commit|[https://github.com/apache/arrow/commit/06fd2da5e8e71b660e6eea4b7702ca175e31f3f5]].
I think the root of the issue comes from the fact that `parquet-mr` writes the
inner struct name as `"element"` by default (see
[here|[https://github.com/apache/parquet-mr/blob/b4198be200e7e2df82bc9a18d54c8cd16aa156ac/parquet-column/src/main/java/org/apache/parquet/schema/ConversionPatterns.java#L33]]),
whereas `parquet-cpp` (or `pyarrow`?) assumes `"item"` (see for example [this
test|[https://github.com/apache/arrow/blob/c805b5fadb548925c915e0e130d6ed03c95d1398/python/pyarrow/tests/test_schema.py#L74]]).
The round-tripping tests write/read in pyarrow only obviously won't catch this.
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