Joris Van den Bossche created ARROW-9009: --------------------------------------------
Summary: [C++][Dataset] ARROW:schema should be removed from schema's metadata when reading Parquet files Key: ARROW-9009 URL: https://issues.apache.org/jira/browse/ARROW-9009 Project: Apache Arrow Issue Type: Bug Components: C++ Reporter: Joris Van den Bossche When reading a parquet file (which was written by Arrow) with the datasets API, it preserves the "ARROW:schema" field in the metadata: {code:python} import pyarrow as pa import pyarrow.parquet as pq import pyarrow.dataset as ds table = pa.table({'a': [1, 2, 3]}) pq.write_table(table, "test.parquet") dataset = ds.dataset("test.parquet", format="parquet") {code} In [7]: dataset.schema Out[7]: a: int64 -- field metadata -- PARQUET:field_id: '1' -- schema metadata -- ARROW:schema: '/////3gAAAAQAAAAAAAKAAwABgAFAAgACgAAAAABAwAMAAAACAAIAAAABA' + 114 In [8]: dataset.to_table().schema Out[8]: a: int64 -- field metadata -- PARQUET:field_id: '1' -- schema metadata -- ARROW:schema: '/////3gAAAAQAAAAAAAKAAwABgAFAAgACgAAAAABAwAMAAAACAAIAAAABA' + 114 {code} while when reading with the `parquet` module reader, we do not preserve this metadata: {code} In [9]: pq.read_table("test.parquet").schema Out[9]: a: int64 -- field metadata -- PARQUET:field_id: '1' {code} Since the "ARROW:schema" information is used to properly reconstruct the Arrow schema from the ParquetSchema, it is no longer needed once you already have the arrow schema, so it's probably not needed to keep it as metadata in the arrow schema. -- This message was sent by Atlassian Jira (v8.3.4#803005)