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[optimize](nereids) allow multi keys for skew join #67300

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[optimize](nereids) allow multi keys for skew join #67300

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xy720 Aug 28, 2026
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58 changes: 31 additions & 27 deletions fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/SkewJoin.java
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Original file line number Diff line number Diff line change
Expand Up @@ -70,7 +70,9 @@ private static Plan transform(MatchingContext<LogicalJoin<Plan, Plan>> ctx) {
LogicalJoin<Plan, Plan> join = ctx.root;
Expression skewExpr = null;
List<Expression> hotValues = new ArrayList<>();
if (join.getHashJoinConjuncts().size() != 1) {
boolean allowMultiKey =
ConnectContext.get().getSessionVariable().isEnableSkewJoinMultiKey();
if (!allowMultiKey && join.getHashJoinConjuncts().size() != 1) {
return null;
}
AbstractPlan left = (AbstractPlan) join.left();
Expand All @@ -82,35 +84,37 @@ private static Plan transform(MatchingContext<LogicalJoin<Plan, Plan>> ctx) {
right.accept(derive, new DeriveContext());
}

EqualPredicate equal = (EqualPredicate) join.getHashJoinConjuncts().get(0);
if (join.left().getOutputSet().contains(equal.right())) {
equal = equal.commute();
}

if (join.getJoinType().isInnerJoin() || join.getJoinType().isLeftOuterJoin()) {
Expression leftEqHand = equal.child(0);
if (left.getStats().findColumnStatistics(leftEqHand) != null) {
ColumnStatistic leftColStats = left.getStats().findColumnStatistics(leftEqHand);
Map<Literal, Float> filtered = StatisticsUtil.getHotValuesWithOriginalThreshold(
leftColStats.getHotValues(), leftColStats.ndv);
if (filtered != null) {
skewExpr = leftEqHand;
hotValues.addAll(filtered.keySet());
}
for (Expression conjunct : join.getHashJoinConjuncts()) {
EqualPredicate equal = (EqualPredicate) conjunct;
if (join.left().getOutputSet().contains(equal.right())) {
equal = equal.commute();
}
} else if (join.getJoinType().isRightOuterJoin()) {
Expression rightEqHand = equal.child(1);
if (right.getStats().findColumnStatistics(rightEqHand) != null) {
ColumnStatistic rightColStats = right.getStats().findColumnStatistics(rightEqHand);
Map<Literal, Float> filtered = StatisticsUtil.getHotValuesWithOriginalThreshold(
rightColStats.getHotValues(), rightColStats.ndv);
if (filtered != null) {
skewExpr = rightEqHand;
hotValues.addAll(filtered.keySet());
Map<Literal, Float> filtered = null;
Expression sideExpr = null;
if (join.getJoinType().isInnerJoin() || join.getJoinType().isLeftOuterJoin()) {
Expression leftEqHand = equal.child(0);
if (left.getStats().findColumnStatistics(leftEqHand) != null) {
ColumnStatistic leftColStats = left.getStats().findColumnStatistics(leftEqHand);
filtered = StatisticsUtil.getHotValuesWithOriginalThreshold(
leftColStats.getHotValues(), leftColStats.ndv);
sideExpr = leftEqHand;
}
} else if (join.getJoinType().isRightOuterJoin()) {
Expression rightEqHand = equal.child(1);
if (right.getStats().findColumnStatistics(rightEqHand) != null) {
ColumnStatistic rightColStats = right.getStats().findColumnStatistics(rightEqHand);
filtered = StatisticsUtil.getHotValuesWithOriginalThreshold(
rightColStats.getHotValues(), rightColStats.ndv);
sideExpr = rightEqHand;
}
} else {
return null;
}
if (filtered != null && !filtered.isEmpty()) {
skewExpr = sideExpr;
hotValues.addAll(filtered.keySet());
break;
}
} else {
return null;
}
if (skewExpr == null || hotValues.isEmpty()) {
return null;
Expand Down
14 changes: 14 additions & 0 deletions fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java
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Original file line number Diff line number Diff line change
Expand Up @@ -326,6 +326,9 @@ public String toString() {
// turn off all automatic join reorder algorithms
public static final String DISABLE_JOIN_REORDER = "disable_join_reorder";

// Allow SkewJoin auto-salt to trigger on joins with more than one hash key.
public static final String ENABLE_SKEW_JOIN_MULTI_KEY = "enable_skew_join_multi_key";

public static final String MAX_JOIN_NUMBER_OF_REORDER = "max_join_number_of_reorder";

public static final String ENABLE_NEREIDS_DML = "enable_nereids_dml";
Expand Down Expand Up @@ -1949,6 +1952,9 @@ public void setCboNetWeight(double cboNetWeight) {
@VarAttrDef.VarAttr(name = DISABLE_JOIN_REORDER)
private boolean disableJoinReorder = false;

@VarAttrDef.VarAttr(name = ENABLE_SKEW_JOIN_MULTI_KEY, needForward = true)
private boolean enableSkewJoinMultiKey = true;

@VarAttrDef.VarAttr(name = MAX_JOIN_NUMBER_OF_REORDER)
private int maxJoinNumberOfReorder = 63;

Expand Down Expand Up @@ -5017,6 +5023,14 @@ public boolean isDisableJoinReorder() {
return disableJoinReorder;
}

public boolean isEnableSkewJoinMultiKey() {
return enableSkewJoinMultiKey;
}

public void setEnableSkewJoinMultiKey(boolean enable) {
this.enableSkewJoinMultiKey = enable;
}

public boolean isEnableBushyTree() {
return enableBushyTree;
}
Expand Down
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