zhuqi-lucas opened a new issue, #21700:
URL: https://github.com/apache/datafusion/issues/21700
## Is your feature request related to a problem or challenge?
When an Extension node (e.g. view matching OneOf) has many children but no
expressions, `LogicalPlan::map_expressions` still clones all inputs and calls
`with_exprs_and_inputs` to reconstruct the node — wasted work since there are
no expressions to transform.
In our production system with view matching (5 MV candidates × ~15 optimizer
rules), this unnecessary rebuild is the dominant cost of the optimizer pass for
plans containing Extension nodes.
## Describe the solution you'd like
Add an early return in `map_expressions` when `node.expressions()` is empty:
```rust
LogicalPlan::Extension(Extension { node }) => {
let raw_exprs = node.expressions();
if raw_exprs.is_empty() {
Transformed::no(LogicalPlan::Extension(Extension { node }))
} else {
// existing clone + rebuild path
}
}
```
## Describe alternatives you've considered
None — the change is straightforward and safe. Empty expressions means no
transform is needed.
## Additional context
Benchmark results (criterion micro-benchmark):
| Children | no_expr (optimized) | with_expr (rebuild) | Speedup |
|----------|--------------------|--------------------|---------|
| 1 | 24 ns | 167 ns | 7x |
| 3 | 23 ns | 192 ns | 8x |
| 5 | 23 ns | 181 ns | 8x |
| 10 | 24 ns | 216 ns | 9x |
The `no_expr` path is constant time regardless of children count.
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