kosiew commented on code in PR #22865:
URL: https://github.com/apache/datafusion/pull/22865#discussion_r3386024891
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datafusion/physical-plan/src/joins/nested_loop_join.rs:
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@@ -2368,25 +2434,20 @@ impl NestedLoopJoinStream {
// Early return if join type can't have unmatched rows
let join_type_no_produce_left =
!need_produce_result_in_final(self.join_type);
- // Early return if another thread is already processing unmatched rows.
+ // Early return if another partition is the designated emitter.
Review Comment:
Nice simplification. Since the invariant is already captured by `ProbeEnd`
and documented on the state/helper, I wonder if this comment and the negated
temporary could be trimmed down a bit.
Something along these lines seems a little easier to scan:
```rust
// `ProbeEnd` already recorded whether this stream emits unmatched-left rows.
let finished = self.left_emit_idx >= left_batch.num_rows();
if join_type_no_produce_left || !self.is_unmatched_left_emitter || finished {
return Ok(false);
}
```
That keeps the emit state focused on the local decision while preserving the
existing behavior.
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