comphead commented on code in PR #17562:
URL: https://github.com/apache/datafusion/pull/17562#discussion_r2349437381
##########
datafusion/physical-plan/src/joins/nested_loop_join.rs:
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@@ -1232,11 +1235,49 @@ impl NestedLoopJoinStream {
// and push the result into output_buffer
// ========
+ // Special case:
+ // When the right batch is very small, join with multiple left rows at
once,
+ //
+ // The regular implementation is not efficient if the plan's right
child is
+ // very small (e.g. 1 row total), because inside the inner loop of
NLJ, it's
+ // handling one input right batch at once, if it's not large enough,
the
+ // overheads like filter evalaution can't be amortized through
vectorization.
Review Comment:
```suggestion
// overheads like filter evalution can't be amortized through
vectorization.
```
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