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

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

    [ https://issues.apache.org/jira/browse/ARROW-11981?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17302515#comment-17302515 ] 

Ben Kietzman commented on ARROW-11981:
--------------------------------------

[~davidli] [~westonpace]

> [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
>            Priority: Major
>              Labels: dataset
>
> 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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