github-actions[bot] commented on code in PR #67941:
URL: https://github.com/apache/doris/pull/67941#discussion_r4003635622
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fe/fe-core/src/main/java/org/apache/doris/planner/SelectNode.java:
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@@ -69,9 +69,14 @@ public boolean isSerialNode() {
public Pair<PlanNode, LocalExchangeType> enforceAndDeriveLocalExchange(
PlanTranslatorContext translatorContext, PlanNode parent,
LocalExchangeTypeRequire parentRequire) {
Pair<PlanNode, LocalExchangeType> enforceResult
- = enforceRequire(translatorContext, children.get(0), 0,
parentRequire);
+ = enforceRequire(translatorContext, children.get(0), 0,
LocalExchangeTypeRequire.noRequire());
this.children = new ArrayList<>();
this.children.add(enforceResult.first);
- return Pair.of(this, enforceResult.second);
+ // Select does not own the parent's hash expressions, so it cannot
prove that an
+ // independently derived child hash distribution uses the same keys.
Report NOOP
+ // for a hash requirement and let the parent enforce its keys above
Select.
+ LocalExchangeType outputType =
parentRequire.preferType().isHashShuffle()
Review Comment:
[P2] Avoid repartitioning an already aligned Select input. A reachable shape
is `HashJoin(k) -> Select(r < 2) -> Project(k, random(0) AS r) -> Union`: the
volatile alias keeps the Select above the projected Union, while the join's
hash property on `k` is propagated to the Union branches. `SetOperationNode`
can therefore report their agreed GLOBAL hash placement, but this line replaces
that proven-aligned result with `NOOP`, so the join adds another GLOBAL local
hash exchange above Select. For a low-selectivity predicate, the extra per-row
hashing/routing, buffering, and pipeline boundary scale with the full input.
Please retain the correctness fence for mismatched or unknown keys, but
carry/compare enough hash-key identity to preserve aligned inputs, and add a
plan-shape test covering both cases.
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