2010YOUY01 commented on code in PR #20228:
URL: https://github.com/apache/datafusion/pull/20228#discussion_r2787267388
##########
datafusion/physical-plan/src/joins/hash_join/exec.rs:
##########
@@ -1476,12 +1517,32 @@ impl ExecutionPlan for HashJoinExec {
filter: dynamic_filter,
build_accumulator: OnceLock::new(),
}),
+ fetch: self.fetch,
});
result = result.with_updated_node(new_node as Arc<dyn
ExecutionPlan>);
}
}
Ok(result)
}
+
+ fn supports_limit_pushdown(&self) -> bool {
+ // Hash join execution plan does not support pushing limit down
through to children
+ // because the children don't know about the join condition and can't
+ // determine how many rows to produce
+ false
+ }
+
+ fn fetch(&self) -> Option<usize> {
+ self.fetch
+ }
+
+ fn with_fetch(&self, limit: Option<usize>) -> Option<Arc<dyn
ExecutionPlan>> {
+ HashJoinExecBuilder::from(self)
Review Comment:
I don't get the purpose of this builder, and why do we have to do a round
trip to set this `fetch`.
Also, the comment on `HashJoinExecBuilder` lacks further explanation. This
API feels quite subtle: it resets several runtime fields (for example, the
dynamic filter), which can be surprising. I would expect more documentation
explaining the intended usage, invariants, and any safety considerations when
using it.
Could we do directly clone like
```rust
Self {
fetch: limit,
// ...explicitly reset not cloneable runtime contents
..self.clone()
}
```
##########
datafusion/physical-plan/src/joins/hash_join/exec.rs:
##########
@@ -760,6 +777,11 @@ impl HashJoinExec {
self.null_equality
}
+ /// Get the fetch (limit) for this join
+ pub fn fetch(&self) -> Option<usize> {
Review Comment:
Is this one needed? I think we already have a equivalent one in `impl
ExecutionPlan for HashJoinExec`
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