[jira] [Commented] (ARROW-15118) [C++] Cast kernel always creates and populates null bitmap

["David Li (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ARROW-15118?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17460072#comment-17460072 ] 

David Li commented on ARROW-15118:
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Or as Antoine noted, we can generalize it and change INTERSECTION to not emit a null bitmap if all inputs have no nulls.

> [C++] Cast kernel always creates and populates null bitmap
> ----------------------------------------------------------
>
>                 Key: ARROW-15118
>                 URL: https://issues.apache.org/jira/browse/ARROW-15118
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: C++
>            Reporter: Eduardo Ponce
>            Priority: Minor
>              Labels: kernel
>             Fix For: 8.0.0
>
>
> Cast kernels seem to always create and populate the null bitmap even if the input data structure had a `nullptr` null bitmap. This automatic and extra allocation is not desirable, and not consistent.
> It seems some cast kernels use COMPUTED_NO_ALLOCATE and others use the default (INTERSECTION). We could change INTERSECTION to be a special-case of one input Array with no null bitmap. The expected behavior is that if the input has no nulls, don't bother emitting a null bitmap.



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