englefly commented on code in PR #54207: URL: https://github.com/apache/doris/pull/54207#discussion_r2275612752
########## fe/fe-core/src/main/java/org/apache/doris/nereids/rules/rewrite/SkewJoin.java: ########## @@ -0,0 +1,118 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +package org.apache.doris.nereids.rules.rewrite; + +import org.apache.doris.nereids.hint.DistributeHint; +import org.apache.doris.nereids.hint.JoinSkewInfo; +import org.apache.doris.nereids.pattern.MatchingContext; +import org.apache.doris.nereids.rules.Rule; +import org.apache.doris.nereids.rules.RuleType; +import org.apache.doris.nereids.rules.rewrite.StatsDerive.DeriveContext; +import org.apache.doris.nereids.trees.expressions.EqualPredicate; +import org.apache.doris.nereids.trees.expressions.Expression; +import org.apache.doris.nereids.trees.plans.AbstractPlan; +import org.apache.doris.nereids.trees.plans.DistributeType; +import org.apache.doris.nereids.trees.plans.Plan; +import org.apache.doris.nereids.trees.plans.logical.LogicalJoin; +import org.apache.doris.qe.ConnectContext; +import org.apache.doris.qe.SessionVariable; + +import java.util.ArrayList; +import java.util.List; + +/** + * When encountering a data-skewed join, there are currently two optimization methods: + * using salt-join or using broadcast join. + * If we detect data skew during the RBO phase and the right table is relatively large, we will automatically add salt. + * + * Depends on InitJoinOrder rule + */ +public class SkewJoin extends OneRewriteRuleFactory { + + @Override + public Rule build() { + return logicalJoin() + .when(join -> join.getJoinType().isOneSideOuterJoin() + || join.getJoinType().isInnerJoin()) + .when(join -> join.getDistributeHint().distributeType == DistributeType.NONE) + .whenNot(LogicalJoin::isMarkJoin) + .thenApply(SkewJoin::transform).toRule(RuleType.SALT_JOIN); + } + + private static Plan transform(MatchingContext<LogicalJoin<Plan, Plan>> ctx) { + StatsDerive derive = new StatsDerive(false); + + LogicalJoin<Plan, Plan> join = ctx.root; + Expression skewExpr = null; + List<Expression> hotValues = new ArrayList<>(); + if (join.getHashJoinConjuncts().size() != 1) { + return null; + } + AbstractPlan left = (AbstractPlan) join.left(); + if (left.getStats() == null) { + left.accept(derive, new DeriveContext()); + } + AbstractPlan right = (AbstractPlan) join.right(); + if (right.getStats() == null) { + right.accept(derive, new DeriveContext()); + } + + if (ConnectContext.get() == null) { + return null; + } + + 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 + && left.getStats().findColumnStatistics(leftEqHand).getHotValues() != null) { + skewExpr = leftEqHand; + hotValues.addAll(left.getStats().findColumnStatistics(leftEqHand).getHotValues().keySet()); + } + } else if (join.getJoinType().isRightOuterJoin()) { + Expression rightEqHand = equal.child(1); + if (right.getStats().findColumnStatistics(rightEqHand) != null + && right.getStats().findColumnStatistics(rightEqHand).getHotValues() != null) { + skewExpr = rightEqHand; + hotValues.addAll(right.getStats().findColumnStatistics(rightEqHand).getHotValues().keySet()); + } + } else { + return null; + } + if (skewExpr == null || hotValues.isEmpty()) { + return null; + } + + SessionVariable sessionVariable = ConnectContext.get().getSessionVariable(); + // broadcast join for small right table + // salt join for large right table + if (right.getStats().getRowCount() < sessionVariable.getBroadcastRowCountLimit() / 100) { + DistributeHint hint = new DistributeHint(DistributeType.BROADCAST_RIGHT); + join.setHint(hint); + return join; + } else { + DistributeHint hint = new DistributeHint(DistributeType.SHUFFLE_RIGHT, + new JoinSkewInfo(skewExpr, hotValues, false)); + join.setHint(hint); + return SaltJoin.transform(join); Review Comment: this rule also need to be applies after EliminateJoinByUnique. -- This is an automated message from the Apache Git Service. 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