[jira] [Created] (ARROW-16431) Improve error message in append_row_groups() when appending disjoint metadata

["Michael Milton (Jira)" <ji...@apache.org>]

Michael Milton created ARROW-16431:
--------------------------------------

             Summary: Improve error message in append_row_groups() when appending disjoint metadata
                 Key: ARROW-16431
                 URL: https://issues.apache.org/jira/browse/ARROW-16431
             Project: Apache Arrow
          Issue Type: Improvement
            Reporter: Michael Milton


Currently if you try to append together metadata from row groups with different schemas (?), you get the following error: 


{code:java}
  File "/home/mmilton/.conda/envs/mmilton/envs/driverpipe/lib/python3.9/site-packages/dask/dataframe/io/parquet/arrow.py", line 52, in _append_row_groups
    metadata.append_row_groups(md)
  File "pyarrow/_parquet.pyx", line 628, in pyarrow._parquet.FileMetaData.append_row_groups
    self._metadata.AppendRowGroups(deref(c_metadata))
RuntimeError: AppendRowGroups requires equal schemas.
{code}

What would be useful here is to actually pass the schema difference in the error object in terms of which columns disagree. This information should _also_ be in the error message.

For example if it said:


{code:java}
RuntimeError: AppendRowGroups requires equal schemas. Column "foo" was previously an int32 but the latest row group is storing it as an int64
{code}





--
This message was sent by Atlassian Jira
(v8.20.7#820007)