[GitHub] [flink] TsReaper commented on a change in pull request #10174: [FLINK-14625][table-planner-blink] Add a rule to eliminate cross join as much as possible without statistics

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TsReaper commented on a change in pull request #10174: [FLINK-14625][table-planner-blink] Add a rule to eliminate cross join as much as possible without statistics
URL: https://github.com/apache/flink/pull/10174#discussion_r347183638
 
 

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 File path: flink-table/flink-table-planner-blink/src/main/java/org/apache/flink/table/planner/plan/rules/logical/EliminateCrossJoinRule.java
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 @@ -0,0 +1,477 @@
+/*
+ * 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.flink.table.planner.plan.rules.logical;
+
+import org.apache.flink.util.Preconditions;
+
+import org.apache.calcite.plan.RelOptRule;
+import org.apache.calcite.plan.RelOptRuleCall;
+import org.apache.calcite.rel.RelNode;
+import org.apache.calcite.rel.core.JoinRelType;
+import org.apache.calcite.rel.rules.LoptMultiJoin;
+import org.apache.calcite.rel.rules.MultiJoin;
+import org.apache.calcite.rel.type.RelDataTypeField;
+import org.apache.calcite.rex.RexBuilder;
+import org.apache.calcite.rex.RexInputRef;
+import org.apache.calcite.rex.RexNode;
+import org.apache.calcite.rex.RexShuttle;
+import org.apache.calcite.rex.RexUtil;
+import org.apache.calcite.sql.SqlKind;
+import org.apache.calcite.tools.RelBuilder;
+import org.apache.calcite.util.ImmutableBitSet;
+import org.apache.calcite.util.mapping.Mappings;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.List;
+
+/**
+ * This rule tries to eliminate cross joins by reordering joins.
+ * The new order of joins are determined with the following steps:
+ *
+ * <p>1. The inputs related with an equi-join filter (= or IS NOT DISTINCT FROM) will be joined first.
+ *       Inputs with smaller indices has higher priority.
+ *
+ * <p>2. The inputs related with other join filters will then be joined.
+ *
+ * <p>3. If not all inner join inputs are joined, they will be joined in input order.
+ *
+ * <p>4. Outer joins are added.
+ */
+public class EliminateCrossJoinRule extends RelOptRule {
+
+	public static final EliminateCrossJoinRule INSTANCE = new EliminateCrossJoinRule();
+
+	private EliminateCrossJoinRule() {
+		super(operand(MultiJoin.class, any()), "EliminateCrossJoinRule");
+	}
+
+	@Override
+	public void onMatch(RelOptRuleCall call) {
+		MultiJoin join = call.rel(0);
+		RelBuilder relBuilder = call.builder();
+
+		if (join.isFullOuterJoin()) {
+			// full outer join, do not reorder joins
+			Preconditions.checkArgument(
+				join.getInputs().size() == 2,
+				"Full outer join must have exactly 2 inputs. This is a bug.");
+
+			relBuilder
+				.push(join.getInput(0))
+				.push(join.getInput(1))
+				.join(JoinRelType.FULL, join.getJoinFilter());
+			if (join.getPostJoinFilter() != null) {
+				relBuilder.filter(join.getPostJoinFilter());
+			}
+		} else {
+			int outerJoinCount = 0;
+			for (int i = 0; i < join.getInputs().size(); i++) {
+				if (join.getJoinTypes().get(i) != JoinRelType.INNER) {
+					outerJoinCount++;
+				}
+			}
+			Preconditions.checkState(
+				outerJoinCount <= 1,
+				"EliminateCrossJoinRule assumes that there is at most 1 outer join " +
+					"in a layer of multi-join, but " + outerJoinCount + " outer joins were found.");
+			if (outerJoinCount == 1) {
+				int numInputs = join.getInputs().size();
+				Preconditions.checkState(
+					join.getJoinTypes().get(0) == JoinRelType.RIGHT ||
+						join.getJoinTypes().get(numInputs - 1) == JoinRelType.LEFT,
+					"EliminateCrossJoinRule assumes that " +
+						"the only left outer join input must locate at the end, or" +
+						"the only right outer join input must locate at the beginning");
+			}
+
+			LoptMultiJoin loptMultiJoin = new LoptMultiJoin(join);
+
+			// try to eliminate cross join
+			Vertex joinVertexTree = multiJoinToJoinVertexTree(loptMultiJoin);
+			Mappings.TargetMapping mapping = joinVertexTreeToJoinRelTree(joinVertexTree, loptMultiJoin, relBuilder);
+
+			// apply post-join filters
+			if (join.getPostJoinFilter() != null) {
+				RexBuilder rexBuilder = join.getCluster().getRexBuilder();
+				relBuilder.filter(mapFilter(join.getPostJoinFilter(), mapping, rexBuilder));
+			}
+
+			// use projections to keep the output of the join unchanged
+			List<RexNode> projects = generateProjection(join, mapping);
+			relBuilder.project(projects);
+		}
+
+		RelNode rel = relBuilder.build();
+		call.transformTo(rel);
+	}
+
+	private Vertex multiJoinToJoinVertexTree(LoptMultiJoin multiJoin) {
+		JoinVertexTreeBuilder builder = new JoinVertexTreeBuilder(
+			multiJoin,
+			(left, right) -> {
+				boolean leftIsEqui = isEquiFilter(left.filter);
+				boolean rightIsEqui = isEquiFilter(right.filter);
+				if (leftIsEqui ^ rightIsEqui) {
+					// one of the filter is not an equi-filter
+					// equi-filter has higher priority
+					return leftIsEqui ? -1 : 1;
+				} else {
+					// both or none of the filter is an equi-filter
+					// the one with the smallest input wins
+					int a = -1;
+					int b = -1;
+					do {
+						a = left.inputBitSet.nextSetBit(a + 1);
+						b = right.inputBitSet.nextSetBit(b + 1);
+					} while (a == b && a >= 0);
+
+					if (a >= 0 && b >= 0) {
+						return a - b;
+					} else if (a < 0 && b < 0) {
+						return 0;
+					} else {
+						return a;
+					}
+				}
+			});
+
+		JoinFilter bestFilter;
+		while ((bestFilter = builder.getBestFilter()) != null) {
+			builder.innerJoin(bestFilter.inputBitSet);
+		}
+
+		return builder.toJoinVertexTree();
+	}
+
+	private boolean isEquiFilter(RexNode filter) {
+		return filter.isA(SqlKind.EQUALS) || filter.isA(SqlKind.IS_NOT_DISTINCT_FROM);
 
 Review comment:
   No, but after this checking we will also check if the left input and right input are both input refs. This will distinguish `a = b` from `a = 1`.

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