jackwener commented on issue #4267:
URL:
https://github.com/apache/arrow-datafusion/issues/4267#issuecomment-1319545030
let me explain why.
Due to global-state exists, we can't just optimize a subtree, we must
traverse the whole tree.
In fact, I prefer to `Pattern-match`, we match a subtree `pattern`, and just
optimize the pattren/subtree.
A example: Merge Limit
```rust
match plan {
Limit => {
match childPlan => {
Limit => { merge(limit, childlimit) }
_ => { don't match pattern, return None or recurse....}
}
}
_ => { don't match pattern, return None or recurse....}
}
```
we just match `limit-limit`, and handle it.
BUT, global-state force we must handle various situations， and we must
traverse the tree all.
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