[ARROW-12873] [C++][Compute] Support tagging ExecBatches with arbitrary extra information

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: C++
• Labels: query-engine
• External issue URL: https://github.com/apache/arrow/issues/18681
• Assignee: Unassigned
• Reporter: Ben Kietzman
• Created: 25/May/21 14:53
• Updated: 11/Jan/23 08:29

Description

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

struct AnySet {
  void* Get(tag_t tag);
  void Set(tag_t tag, void* value, FnOnce<void(void*)> destructor);
};

Issue Links

• blocks: ARROW-12710 [C++] String concatenate aggregate kernel
• is a child of: ARROW-12633 [C++] Query engine umbrella issue