kosiew commented on code in PR #23359:
URL: https://github.com/apache/datafusion/pull/23359#discussion_r3577142697
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datafusion/physical-plan/src/sorts/sort_preserving_merge.rs:
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@@ -382,7 +382,9 @@ impl ExecutionPlan for SortPreservingMergeExec {
}
fn statistics_with_args(&self, args: &StatisticsArgs) ->
Result<Arc<Statistics>> {
- args.compute_child_statistics(&self.input, None)
+ let stats =
+ Arc::unwrap_or_clone(args.compute_child_statistics(&self.input,
None)?);
+ Ok(Arc::new(stats.with_fetch(self.fetch, 0, 1)?))
}
fn supports_limit_pushdown(&self) -> bool {
Review Comment:
Would it make sense to also override `cardinality_effect()` here, returning
`LowerEqual` when `self.fetch.is_some()` and `Equal` otherwise, similar to
`SortExec`? This PR correctly fixes the statistics-based costing, but
`SortPreservingMergeExec` with a fetch still reports the default `Unknown`
cardinality effect. As a result, optimizer logic that relies on cardinality
metadata instead of statistics may not see the same fetch-aware behavior.
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