mihaibudiu commented on code in PR #4619: URL: https://github.com/apache/calcite/pull/4619#discussion_r2572271717
########## core/src/main/java/org/apache/calcite/sql2rel/TopDownGeneralDecorrelator.java: ########## @@ -0,0 +1,1009 @@ +/* + * 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.calcite.sql2rel; + +import org.apache.calcite.plan.RelOptUtil; +import org.apache.calcite.plan.Strong; +import org.apache.calcite.plan.hep.HepPlanner; +import org.apache.calcite.plan.hep.HepProgram; +import org.apache.calcite.rel.RelCollation; +import org.apache.calcite.rel.RelNode; +import org.apache.calcite.rel.core.Aggregate; +import org.apache.calcite.rel.core.AggregateCall; +import org.apache.calcite.rel.core.Correlate; +import org.apache.calcite.rel.core.CorrelationId; +import org.apache.calcite.rel.core.Filter; +import org.apache.calcite.rel.core.Join; +import org.apache.calcite.rel.core.JoinRelType; +import org.apache.calcite.rel.core.Project; +import org.apache.calcite.rel.core.SetOp; +import org.apache.calcite.rel.core.Sort; +import org.apache.calcite.rel.rules.CoreRules; +import org.apache.calcite.rel.type.RelDataType; +import org.apache.calcite.rex.RexCall; +import org.apache.calcite.rex.RexCorrelVariable; +import org.apache.calcite.rex.RexFieldAccess; +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.rex.RexWindow; +import org.apache.calcite.sql.SqlAggFunction; +import org.apache.calcite.sql.SqlKind; +import org.apache.calcite.sql.fun.SqlCountAggFunction; +import org.apache.calcite.sql.fun.SqlStdOperatorTable; +import org.apache.calcite.sql2rel.RelDecorrelator.CorDef; +import org.apache.calcite.sql2rel.RelDecorrelator.Frame; +import org.apache.calcite.tools.RelBuilder; +import org.apache.calcite.util.ImmutableBitSet; +import org.apache.calcite.util.Litmus; +import org.apache.calcite.util.Pair; +import org.apache.calcite.util.ReflectUtil; +import org.apache.calcite.util.ReflectiveVisitor; +import org.apache.calcite.util.mapping.Mappings; + +import com.google.common.collect.ImmutableList; +import com.google.common.collect.ImmutableSet; + +import org.checkerframework.checker.nullness.qual.Nullable; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.HashMap; +import java.util.List; +import java.util.Map; +import java.util.NavigableMap; +import java.util.NavigableSet; +import java.util.Set; +import java.util.TreeMap; +import java.util.TreeSet; +import java.util.stream.IntStream; + +import static java.util.Objects.requireNonNull; + +/** + * A top‑down, generic decorrelation algorithm that can handle deep nestings of correlated + * subqueries and that generalizes to complex query constructs. More details are in paper: + * <a href="https://dl.gi.de/items/b9df4765-d1b0-4267-a77c-4ce4ab0ee62d";> + * Improving Unnesting of Complex Queries</a> + */ +public class TopDownGeneralDecorrelator implements ReflectiveVisitor { + + private final RelBuilder builder; + + // record the CorDef in the current context (including those in the parent Correlate). + private final NavigableSet<CorDef> corDefs; + + // a map from RelNode to whether existing correlated expressions (according to corDefs). + private final Map<RelNode, Boolean> hasCorrelatedExpressions; + + // a map from RelNode to its UnnestQuery. + private final Map<RelNode, UnnestQuery> mapRelToUnnestQuery; + + private final boolean hasParent; + + // whether allow empty output resulting from decorrelate rewriting. + private boolean emptyOutputDisable; + + // the domain of the free variables (i.e. corDefs) D, it's duplicate free. + private DedupFreeVarsNode dedupFreeVarsNode; + + @SuppressWarnings("method.invocation.invalid") + private final ReflectUtil.MethodDispatcher<RelNode> dispatcher = + ReflectUtil.createMethodDispatcher( + RelNode.class, getVisitor(), "unnestInternal", RelNode.class); + + @SuppressWarnings("initialization.fields.uninitialized") + public TopDownGeneralDecorrelator( + RelBuilder builder, + boolean hasParent, + boolean emptyOutputDisable, + @Nullable Set<CorDef> parentCorDefs, + @Nullable Map<RelNode, Boolean> parentHasCorrelatedExpressions, + @Nullable Map<RelNode, UnnestQuery> parentMapRelToUnnestInfo) { + this.builder = builder; + this.hasParent = hasParent; + this.emptyOutputDisable = emptyOutputDisable; + this.corDefs = new TreeSet<>(); + if (parentCorDefs != null) { + this.corDefs.addAll(parentCorDefs); + } + this.hasCorrelatedExpressions = parentHasCorrelatedExpressions == null + ? new HashMap<>() + : parentHasCorrelatedExpressions; + this.mapRelToUnnestQuery = parentMapRelToUnnestInfo == null + ? new HashMap<>() + : parentMapRelToUnnestInfo; + } + + private static TopDownGeneralDecorrelator createEmptyDecorrelator(RelBuilder builder) { + return new TopDownGeneralDecorrelator(builder, false, false, null, null, null); + } + + private TopDownGeneralDecorrelator createSubDecorrelator() { + TopDownGeneralDecorrelator subDecorrelator = + new TopDownGeneralDecorrelator( + builder, + true, + emptyOutputDisable, + corDefs, + hasCorrelatedExpressions, + mapRelToUnnestQuery); + subDecorrelator.dedupFreeVarsNode = this.dedupFreeVarsNode; + return subDecorrelator; + } + + /** + * Decorrelates a query. This is the entry point for this class. + * + * @param rel Root node of the query + * @param builder RelBuilder + * @return Equivalent node without correlation + */ + public static RelNode decorrelateQuery(RelNode rel, RelBuilder builder) { + HepProgram preProgram = HepProgram.builder() + .addRuleCollection( + ImmutableList.of( + CoreRules.FILTER_PROJECT_TRANSPOSE, + CoreRules.FILTER_INTO_JOIN, + CoreRules.FILTER_CORRELATE)) + .build(); + HepPlanner prePlanner = new HepPlanner(preProgram); + prePlanner.setRoot(rel); + RelNode preparedRel = prePlanner.findBestExp(); + + // start decorrelating + TopDownGeneralDecorrelator decorrelator = createEmptyDecorrelator(builder); + RelNode decorrelateNode = rel; + try { + decorrelateNode = decorrelator.correlateElimination(preparedRel); + } catch (UnsupportedOperationException e) { + // if the correlation exists in an unsupported operator, retain the original plan. + } + + HepProgram postProgram = HepProgram.builder() + .addRuleCollection( + ImmutableList.of( + CoreRules.FILTER_PROJECT_TRANSPOSE, + CoreRules.FILTER_INTO_JOIN, + CoreRules.MARK_TO_SEMI_OR_ANTI_JOIN_RULE, + CoreRules.PROJECT_MERGE, + CoreRules.PROJECT_REMOVE)) + .build(); + HepPlanner postPlanner = new HepPlanner(postProgram); + postPlanner.setRoot(decorrelateNode); + return postPlanner.findBestExp(); + } + + /** + * Eliminates Correlate. + * + * @param rel RelNode + * @return Equivalent RelNode without Correlate + */ + private RelNode correlateElimination(RelNode rel) { + if (rel instanceof Correlate) { + final Correlate correlate = (Correlate) rel; + final RelNode newLeft; + if (hasParent) { + // if the current decorrelator has a parent, it means that the Correlate must have + // correlation from above. + assert hasCorrelatedExpressions.containsKey(correlate) + && hasCorrelatedExpressions.get(correlate); + newLeft = unnest(correlate.getLeft()); + } else { + // otherwise, start a new decorrelation for the left side. + newLeft = decorrelateQuery(correlate.getLeft(), builder); + } + + // create or update UnnestQuery of left side and corDefs of this decorrelator. + UnnestQuery leftInfo = mapRelToUnnestQuery.get(correlate.getLeft()); + TreeMap<CorDef, Integer> corDefOutputs = new TreeMap<>(); + Map<Integer, Integer> oldToNewOutputs = new HashMap<>(); + for (int i = 0; i < correlate.getLeft().getRowType().getFieldCount(); i++) { + int newColumnIndex = leftInfo == null ? i : requireNonNull(leftInfo.oldToNewOutputs.get(i)); + oldToNewOutputs.put(i, newColumnIndex); + if (correlate.getRequiredColumns().get(i)) { + CorDef corDef = new CorDef(correlate.getCorrelationId(), i); + corDefs.add(corDef); + corDefOutputs.put(corDef, newColumnIndex); + } + } + if (leftInfo != null) { + corDefOutputs.putAll(leftInfo.corDefOutputs); + } + leftInfo = new UnnestQuery(correlate.getLeft(), newLeft, corDefOutputs, oldToNewOutputs); + dedupFreeVarsNode = generateDedupFreeVarsNode(newLeft, leftInfo); + + // decorrelate right side + detectCorrelatedExpressions(correlate.getRight()); + emptyOutputDisable |= correlate.getJoinType() == JoinRelType.MARK; + RelNode newRight = unnest(correlate.getRight()); + UnnestQuery rightInfo = requireNonNull(mapRelToUnnestQuery.get(correlate.getRight())); + + // rewrite condition, adding the natural join condition between the left side and + // the domain D that in right side. + // + // Correlate(condition=[p]) + // / \ + // L ... with correlation + // \ + // R + // => + // Join(condition=[p AND (L is not distinct from D)]) + // / \ + // L ... without correlation + // \ + // x + // / \ + // D R + builder.push(newLeft).push(newRight); + RexNode unnestedJoinCondition = + createUnnestedJoinCondition(correlate.getCondition(), leftInfo, rightInfo, true); + RelNode unnestedRel = builder.join(correlate.getJoinType(), unnestedJoinCondition).build(); + + if (!hasParent) { + // ensure that the fields are in the same order as in the original plan. + builder.push(unnestedRel); + UnnestQuery unnestQuery = + createJoinUnnestInfo( + leftInfo, + rightInfo, + correlate, + unnestedRel, + correlate.getJoinType()); + List<RexNode> projects + = builder.fields(new ArrayList<>(unnestQuery.oldToNewOutputs.values())); + unnestedRel = builder.project(projects).build(); + } + return unnestedRel; + } else { + for (int i = 0; i < rel.getInputs().size(); i++) { + rel.replaceInput(i, correlateElimination(rel.getInput(i))); + } + } + return rel; + } + + /** + * Generate the domain of the free variables D. + * + * @param newLeft the left side (without correlation) of Correlate + * @param leftInfo the UnnestQuery of the left side of Correlate + * @return the domain of the free variables D + */ + private DedupFreeVarsNode generateDedupFreeVarsNode(RelNode newLeft, UnnestQuery leftInfo) { + List<Integer> columnIndexes = new ArrayList<>(); + for (CorDef corDef : corDefs) { + int fieldIndex = requireNonNull(leftInfo.corDefOutputs.get(corDef)); + columnIndexes.add(fieldIndex); + } + List<RexNode> inputRefs = builder.push(newLeft) + .fields(columnIndexes); + RelNode rel = builder.project(inputRefs).distinct().build(); + return new DedupFreeVarsNode(rel); + } + + /** + * Detects whether existing correlated expressions in the RelNode (according to corDefs). + * + * @param rel RelNode + * @return true when there are correlated expressions + */ + private boolean detectCorrelatedExpressions(RelNode rel) { + boolean hasCorrelation = false; Review Comment: I was specifically considering the case when the Rel object is not a tree, but a DAG. -- This is an automated message from the Apache Git Service. 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