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);
};

Reporter: Ben Kietzman / @bkietz

Related issues:

• [C++] String concatenate aggregate kernel (blocks)
• [C++] Query engine umbrella issue (is a child of)

_{Note: This issue was originally created as ARROW-12873. Please see the migration documentation for further details.}