ASAP-aware mapping should make its discovered opportunities visible to users and other components.
For each relevant region of the plan, the planner should be able to explain:
- which replacements exist,
- what alternatives each replacement introduces,
- what conditions make those alternatives legal,
- and which parts of the plan they affect.
For example:
Aggregation: Quantile(latency, 0.99)
Available alternatives:
- exact quantile
- KLL
- DDSketch
Additional opportunities:
- share source filtering with Query B
- reuse finer-grained aggregation through roll-up
Implemented as asap-aware-mapping's explanation module (explain_replacements/explain_replacements_with, issue #257)