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https://issues.apache.org/jira/browse/ARROW-12873?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17351918#comment-17351918
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Ben Kietzman commented on ARROW-12873:
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It's worth noting that without some support for tagging we won't be able to
maintain batch order for simple filter+project workflows, which is currently
required by ParquetDataset. Currently this is handled in dataset:: by tagging
batches with the indices of their origin fragment and their index within that
fragment, then stitching batches back into a table which maintains the original
batch order.
> [C++][Compute] Support tagging ExecBatches with arbitrary extra information
> ---------------------------------------------------------------------------
>
> Key: ARROW-12873
> URL: https://issues.apache.org/jira/browse/ARROW-12873
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++
> Reporter: Ben Kietzman
> Priority: Major
>
> Ideally, ExecBatches could be tagged with arbitrary optional objects for
> tracing purposes and to transmit execution hints from one ExecNode to another.
> These should *not* be explicit members like ExecBatch::selection_vector is,
> since they may not originate from the arrow library. For an example within
> the arrow project: {{libarrow_dataset}} will be used to produce ScanNodes and
> a WriteNodes and it's useful to tag scanned batches with their {{Fragment}}
> of origin. However adding {{ExecBatch::fragment}} would result in a cyclic
> dependency.
> To facilitate this tagging capability, we would need a type erased container
> something like
> {code}
> struct AnySet {
> void* Get(tag_t tag);
> void Set(tag_t tag, void* value, FnOnce<void(void*)> destructor);
> };
> {code}
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