walterddr commented on code in PR #11976: URL: https://github.com/apache/pinot/pull/11976#discussion_r1391317172
########## pinot-query-planner/src/main/java/org/apache/calcite/rel/rules/PinotRelDistributionTraitRule.java: ########## @@ -0,0 +1,178 @@ +/** + * 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.rel.rules; + +import com.google.common.collect.ImmutableList; +import java.util.ArrayList; +import java.util.List; +import org.apache.calcite.plan.RelOptRule; +import org.apache.calcite.plan.RelOptRuleCall; +import org.apache.calcite.plan.RelTrait; +import org.apache.calcite.plan.RelTraitSet; +import org.apache.calcite.rel.RelDistribution; +import org.apache.calcite.rel.RelDistributions; +import org.apache.calcite.rel.RelNode; +import org.apache.calcite.rel.core.Exchange; +import org.apache.calcite.rel.hint.PinotHintOptions; +import org.apache.calcite.rel.hint.PinotHintStrategyTable; +import org.apache.calcite.rel.logical.LogicalAggregate; +import org.apache.calcite.rel.logical.LogicalFilter; +import org.apache.calcite.rel.logical.LogicalJoin; +import org.apache.calcite.rel.logical.LogicalProject; +import org.apache.calcite.rel.logical.LogicalTableScan; +import org.apache.calcite.rel.logical.PinotLogicalExchange; +import org.apache.calcite.tools.RelBuilderFactory; +import org.apache.calcite.util.mapping.Mappings; +import org.apache.pinot.query.planner.plannode.AggregateNode; +import org.checkerframework.checker.nullness.qual.Nullable; + + +/** + * Special rule for Pinot, this rule populates {@link RelDistribution} across the entire relational tree. + * + * we implement this rule as a workaround b/c {@link org.apache.calcite.plan.RelTraitPropagationVisitor}, which is + * deprecated. The idea is to associate every node with a RelDistribution derived from {@link RelNode#getInputs()} + * or from the node itself (via hints, or special handling of the type of node in question). + */ +public class PinotRelDistributionTraitRule extends RelOptRule { Review Comment: this is a good point. i think the entire way of how we handle distribution and exchanges needs to be revisited Status quo === we currently 1. explicitly insert *logical* exchanges where we *might* require data shuffling; and 2. then determine whether those exchanges are real data shuffle or possible passthrough; 3. then we determine whether to assign more/less servers to run either side of the exchanges Current solution === This PR only addresses step-2: to give it a better idea on whether the RelDistribution is the same before & after an exchange. for this purpose, it is OK (at this point) to only keep one of the 2 sides for JOIN Rel. Needs revisit === there are several problems 1. should we explicitly insert exchange or should we use other abstractions? - there are other ways to add exchange nodes that are more "Calcite-suggested" when managing the Exchange insert instead of applying them during optimization IMO. 2. should the exchange insert be RelDistribution-based or physical-based? - we are mixing the concept of Exchange usage: it can mean (1) altering logical RelDistribution, (2) indicating there potentially could be physical layout differences, (3) whether we can apply leaf-stage optimization - although (3) will be addressed by #11937, we should consider whether to still use ExchangeNode as our abstraction or create our own to avoid confusion 3. should we apply RelDistribution trait before or after Exchange insert - currently we have to do this after insert, but technically if we addresses question (2) we can potentially apply that beforehand ultimately utilizing Exchange was a quick decision during early stage multi-stage engine development and it might not have been the best option. it is worth taking some time to revisit -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
