vrajat commented on code in PR #14296:
URL: https://github.com/apache/pinot/pull/14296#discussion_r1815439888
##########
pinot-query-planner/src/main/java/org/apache/pinot/query/planner/plannode/PlanNodeVisitor.java:
##########
@@ -63,4 +63,150 @@ public interface PlanNodeVisitor<T, C> {
T visitExchange(ExchangeNode exchangeNode, C context);
T visitExplained(ExplainedNode node, C context);
+
+ /**
Review Comment:
Why did you choose to add this class to the same file ?
##########
pinot-query-planner/src/main/java/org/apache/pinot/query/planner/logical/EquivalentStagesFinder.java:
##########
@@ -0,0 +1,339 @@
+/**
+ * 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.pinot.query.planner.logical;
+
+import com.google.common.base.Preconditions;
+import java.util.List;
+import java.util.Objects;
+import org.apache.pinot.query.planner.plannode.AggregateNode;
+import org.apache.pinot.query.planner.plannode.ExchangeNode;
+import org.apache.pinot.query.planner.plannode.ExplainedNode;
+import org.apache.pinot.query.planner.plannode.FilterNode;
+import org.apache.pinot.query.planner.plannode.JoinNode;
+import org.apache.pinot.query.planner.plannode.MailboxReceiveNode;
+import org.apache.pinot.query.planner.plannode.MailboxSendNode;
+import org.apache.pinot.query.planner.plannode.PlanNode;
+import org.apache.pinot.query.planner.plannode.PlanNodeVisitor;
+import org.apache.pinot.query.planner.plannode.ProjectNode;
+import org.apache.pinot.query.planner.plannode.SetOpNode;
+import org.apache.pinot.query.planner.plannode.SortNode;
+import org.apache.pinot.query.planner.plannode.TableScanNode;
+import org.apache.pinot.query.planner.plannode.ValueNode;
+import org.apache.pinot.query.planner.plannode.WindowNode;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * This utility class can be used to find equivalent stages in the query plan.
+ *
+ * Equivalent stages are stages that represent the same job to be done. These
stages can be potentially optimized to
+ * execute that job only once in a special stage that broadcast the results to
all the equivalent stages.
+ */
+public class EquivalentStagesFinder {
+ public static final Logger LOGGER =
LoggerFactory.getLogger(EquivalentStagesFinder.class);
+
+ private EquivalentStagesFinder() {
+ }
+
+ public static GroupedStages findEquivalentStages(MailboxSendNode root) {
+ Visitor visitor = new Visitor();
+ root.visit(visitor, null);
+
+ return visitor._equivalentStages;
+ }
+
+ /**
+ * A visitor that iterates the plan tree and finds equivalent stages.
+ *
+ * It may be a bit confusing that this class, which ends up being a visitor,
calls another visitor to compare nodes.
+ * The reason is that this object implements visitor to iterate the plan
tree in pre-order. Then for each
+ * mailbox send node (which are always the root of a stage), it calls
+ * {@link NodeEquivalence#areEquivalent(MailboxSendNode, MailboxSendNode)}.
NodeEquivalence is another class that
+ * implements visitor, but this time to compare two nodes.
+ */
+ private static class Visitor extends PlanNodeVisitor.DepthFirstVisitor<Void,
Void> {
+ private final GroupedStages.Mutable _equivalentStages = new
GroupedStages.Mutable();
+ private final NodeEquivalence _nodeEquivalence = new NodeEquivalence();
+
+ @Override
+ public Void visitMailboxSend(MailboxSendNode node, Void context) {
+ // It is important to visit children before doing anything.
+ // This is a requirement on NodeEquivalence.areEquivalent() method that
reduce the complexity of the algorithm
+ // from O(n^3) to O(n^2).
+ visitChildren(node, context);
+
+ // first try to find if the current node/stage is equivalent to an
already equivalent stages.
+ for (MailboxSendNode uniqueStage : _equivalentStages.getLeaders()) {
+ if (_nodeEquivalence.areEquivalent(node, uniqueStage)) {
+ _equivalentStages.addToGroup(uniqueStage, node);
+ return null;
+ }
+ }
+ // there is no visited stage that is equivalent to the current stage, so
add it to the unique visited stages.
+ _equivalentStages.addNewGroup(node);
+ return null;
+ }
+
+ /**
+ * A visitor that compares two nodes to see if they are equivalent.
+ *
+ * The implementation uses the already visited stages (stored in {@link
#_equivalentStages}) to avoid comparing the
+ * same nodes multiple times. The side effect of that is that the second
argument for {@link #areEquivalent} must be
+ * a node that was already visited.
+ */
+ private class NodeEquivalence implements PlanNodeVisitor<Boolean,
PlanNode> {
Review Comment:
I need to step through patch to understand. Where is the return value
(Boolean) checked ?
Also when are methods like `visitAggregate` called as I cannot find
`visitChildren` calls in the `NodeEquivalence` class.
##########
pinot-query-planner/src/test/java/org/apache/pinot/query/planner/logical/EquivalentStagesFinderTest.java:
##########
@@ -0,0 +1,202 @@
+/**
+ * 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.pinot.query.planner.logical;
+
+import java.util.Map;
+import org.apache.pinot.common.utils.DataSchema;
+import org.apache.pinot.query.planner.plannode.MailboxSendNode;
+import org.testng.annotations.Test;
+
+import static org.testng.Assert.*;
+
+
+public class EquivalentStagesFinderTest extends StagesTestBase {
Review Comment:
Confused by the these tests. Are the tests dependent on each other ? Every
test adds another stage to `_stages` ?
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