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https://issues.apache.org/jira/browse/ARROW-4076?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16724956#comment-16724956
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Uwe L. Korn commented on ARROW-4076:
------------------------------------
I'm ok with this but be aware that having non compatible schemas in a single
dataset is prone to error out a lot more times.
My main motivation for supporting this is, that this probably also means a
small performance improvement as we check a lot less schemas
> [Python] schema validation and filters
> --------------------------------------
>
> Key: ARROW-4076
> URL: https://issues.apache.org/jira/browse/ARROW-4076
> Project: Apache Arrow
> Issue Type: Bug
> Components: Python
> Reporter: George Sakkis
> Priority: Minor
>
> Currently [schema
> validation|https://github.com/apache/arrow/blob/758bd557584107cb336cbc3422744dacd93978af/python/pyarrow/parquet.py#L900]
> of {{ParquetDataset}} takes place before filtering. This may raise a
> {{ValueError}} if the schema is different in some dataset pieces, even if
> these pieces would be subsequently filtered out. I think validation should
> happen after filtering to prevent such spurious errors:
> {noformat}
> --- a/pyarrow/parquet.py
> +++ b/pyarrow/parquet.py
> @@ -878,13 +878,13 @@
> if split_row_groups:
> raise NotImplementedError("split_row_groups not yet implemented")
>
> - if validate_schema:
> - self.validate_schemas()
> -
> if filters is not None:
> filters = _check_filters(filters)
> self._filter(filters)
>
> + if validate_schema:
> + self.validate_schemas()
> +
> def validate_schemas(self):
> open_file = self._get_open_file_func()
> {noformat}
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