yogesh garg created ARROW-4516:
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Summary: Error while creating a ParquetDataset on a path without
`_common_dataset` but with an empty `_tempfile`
Key: ARROW-4516
URL: https://issues.apache.org/jira/browse/ARROW-4516
Project: Apache Arrow
Issue Type: Bug
Components: Python
Affects Versions: 0.12.0
Reporter: yogesh garg
I suspect that there's an error in this line of code:
https://github.com/apache/arrow/blob/master/python/pyarrow/parquet.py#L926
While validating schema in the initialisation of a {{ParquetDataset}}, we
assume that if {{_common_metadata}} file does not exist, the schema should be
inferred from the first piece of that dataset. The first piece, in my
experience, could refer to a file named with an underscore, that does not
necessarily have to contain the schema, and could be an empty file, e.g.
{{_tempfile}}.
{code:bash}
/tmp/pq/
├── part1.parquet
└── _tempfile
{code}
This behavior is allowed by the parquet specification, and we should probably
ignore such pieces.
On a cursory look, we could do either of the following.
1. Choose the first piece with path that does not start with "_"
2. Sort pieces by name, but put all the "_" pieces later while making the
manifest.
https://github.com/apache/arrow/blob/master/python/pyarrow/parquet.py#L729
3. Silently exclude all the files starting with "_" here, but this will need to
be tested:
https://github.com/apache/arrow/blob/master/python/pyarrow/parquet.py#L770
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