[ARROW-8647] [C++][Dataset] Optionally encode partition field values as dictionary type

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.0.0
• Component/s: C++
• Labels: dataset dataset-dask-integration pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/24808
• Assignee: Ben Kietzman
• Reporter: Joris Van den Bossche
• Created: 30/Apr/20 13:35
• Updated: 11/Jan/23 08:01
• Resolved: 30/Jun/20 13:55

Description

In the Python ParquetDataset implementation, the partition fields are returned as dictionary type columns.

In the new Dataset API, we now use a plain type (integer or string when inferred). But, you can already manually specify that the partition keys should be dictionary type by specifying the partitioning schema (in Partitioning passed to the dataset factory).

Since using dictionary type can be more efficient (since partition keys will typically be repeated values in the resulting table), it might be good to still have an option in the DatasetFactory to use dictionary types for the partition fields.

See also https://github.com/apache/arrow/pull/6303#discussion_r400622340

Issue Links

• relates to: ARROW-9288 [C++][Dataset] Discovery of partition field as dictionary type segfaulting with HivePartitioning
• links to: GitHub Pull Request #7536