gabotechs commented on code in PR #20331:
URL: https://github.com/apache/datafusion/pull/20331#discussion_r2851878804
##########
datafusion/physical-optimizer/src/enforce_distribution.rs:
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@@ -1454,21 +1481,87 @@ pub fn ensure_distribution(
plan.with_new_children(children_plans)?
};
+ /// Helper to describe partitioning scheme for error messages
+ fn partitioning_scheme_name(is_repartitioned: bool) -> &'static str {
+ if is_repartitioned {
+ "hash-repartitioned"
+ } else {
+ "file-grouped"
+ }
+ }
+
+ // For partitioned hash joins, decide dynamic filter routing mode.
+ //
+ // Dynamic filtering requires matching partitioning schemes on both sides:
+ // - PartitionIndex: Both sides use file-grouped partitioning
(value-based).
+ // Partition i on build corresponds to partition i on probe by partition
value.
+ // - CaseHash: Both sides use hash repartitioning (hash-based).
+ // Uses CASE expression with hash(row) % N to route to correct partition
filter.
+ //
+ // NOTE: If partitioning schemes are misaligned (one file-grouped, one
hash-repartitioned),
+ // the partitioned join itself is incorrect.
+ // Partition assignments don't match:
+ // - File-grouped: partition 0 = all rows where column="A" (value-based)
+ // - Hash-repartitioned: partition 0 = all rows where hash(column) % N ==
0 (hash-based)
+ // These are incompatible, so the join will miss matching rows.
+ plan = if let Some(hash_join) =
plan.as_any().downcast_ref::<HashJoinExec>()
Review Comment:
Pretty smart and clean way of propagating wether data is getting
repartitioned across steps :+1:
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