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