comphead opened a new issue, #21771:
URL: https://github.com/apache/datafusion/issues/21771
### Is your feature request related to a problem or challenge?
Existing docs:
- docs/source/library-user-guide/query-optimizer.md — good high-level
overview of the optimizer architecture + how to write custom rules. Does NOT
list/describe individual built-in rules.
- datafusion/optimizer/README.md and
datafusion/physical-optimizer/README.md — brief crate-level READMEs, mostly
pointers to the above doc and blog posts.
- working-with-exprs.md and extending-operators.md — touch on optimizer
rules tangentially.
The gap: There is no reference doc that lists and describes what each
built-in rule actually does. The codebase has 27 logical optimizer rules (e.g.,
push_down_filter, eliminate_cross_join,
common_subexpr_eliminate) and 21 physical optimizer rules (e.g.,
join_selection, enforce_sorting, topk_aggregation), but the only way to learn
what each one does is to read the source or use EXPLAIN
VERBOSE.
So query-optimizer.md is good for "how the optimizer works" and "how to
extend it," but it's not enough if you want a reference of "what optimizations
does DataFusion apply and what does each one do."
That reference doesn't exist yet.
### Describe the solution you'd like
_No response_
### Describe alternatives you've considered
_No response_
### Additional context
_No response_
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