EeshanBembi commented on code in PR #16905:
URL: https://github.com/apache/datafusion/pull/16905#discussion_r2233562643
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datafusion/core/src/physical_planner.rs:
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@@ -886,6 +887,26 @@ impl DefaultPhysicalPlanner {
"SortExec requires at least one sort expression"
);
};
+
+ // Check if we can use PartialSortExec instead of SortExec
Review Comment:
We do still need this in the planner. EnforceSorting is a bottom‑up
optimizer that only looks at each SortExec and its direct child, so it can’t
see sibling branches under a UnionExec to ensure they all use the same
partial‑sort strategy. UnionExec itself merely concatenates sorted inputs
without merging, so mixing full and partial sorts would break downstream merge
semantics. By contrast, DefaultPhysicalPlanner builds each subtree top‑down and
knows when two sorts feed into the same UnionExec, allowing it to inject a
uniform PartialSortExec and preserve correct SortPreservingMergeExec behavior.
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