[jira] [Created] (ARROW-11981) [C++][Dataset][Compute] Replace UnionDataset with Union ExecNode

["Ben Kietzman (Jira)" <ji...@apache.org>]

Ben Kietzman created ARROW-11981:
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             Summary: [C++][Dataset][Compute] Replace UnionDataset with Union ExecNode
                 Key: ARROW-11981
                 URL: https://issues.apache.org/jira/browse/ARROW-11981
             Project: Apache Arrow
          Issue Type: Improvement
          Components: C++
    Affects Versions: 3.0.0
            Reporter: Ben Kietzman


UnionDataset allows Fragments of multiple schemas and differing file formats to be scanned together as a single Dataset. This is useful functionality but makes the Dataset interface somewhat difficult to reason about since it must be general enough to accommodate UnionDataset.

After ARROW-11928 it will probably be more natural to support unioning of datasets through a subclass of ExecNode. Reconciliation of differing schemas can then be trivially handled by a full ProjectNode.

Note this would obviate both ARROW-11001 and ARROW-11749. In addition, Dataset could be simplified to a concrete class containing a set of compatibly typed/formatted Fragments.




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