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https://issues.apache.org/jira/browse/CALCITE-5503?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17706342#comment-17706342
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Benchao Li commented on CALCITE-5503:
-------------------------------------
[~zstan] We do not encourage to comment on the closed issues, if there are
problems with the latest main branch, you can log another Jira to describe the
problem. If it's related to this one, just link it as "is related to".
> CheapestPlanReplacer should reuse repeated nodes in a DAG plan
> --------------------------------------------------------------
>
> Key: CALCITE-5503
> URL: https://issues.apache.org/jira/browse/CALCITE-5503
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Moritz Mack
> Assignee: Moritz Mack
> Priority: Minor
> Labels: pull-request-available
> Fix For: 1.34.0
>
> Time Spent: 1h 10m
> Remaining Estimate: 0h
>
> When using CheapestPlanReplacer, semantics of a RelNode tree change if it
> contains the same node multiple times in case this node has inputs itself
> that have to be replaced. During replacement such nodes get copied on each
> occurrence.
> Instead CheapestPlanReplacer should memoize previously visited nodes and emit
> the same result again in the that case.
> The test case below illustrates the issue and fails on the current main
> branch.
>
> {code:java}
> @Test void testMemoizeInputRelNodes() {
> VolcanoPlanner planner = new VolcanoPlanner();
> planner.addRelTraitDef(ConventionTraitDef.INSTANCE);
> RelOptCluster cluster = newCluster(planner);
> // The rule that triggers the assert rule
> planner.addRule(PhysLeafRule.INSTANCE);
> planner.addRule(GoodSingleRule.INSTANCE);
> // Leaf RelNode
> NoneLeafRel leafRel = new NoneLeafRel(cluster, "a");
> RelNode leafPhy = planner
> .changeTraits(leafRel, cluster.traitSetOf(PHYS_CALLING_CONVENTION));
> // RelNode with leaf RelNode as single input
> NoneSingleRel singleRel = new NoneSingleRel(cluster, leafPhy);
> RelNode singlePhy = planner
> .changeTraits(singleRel, cluster.traitSetOf(PHYS_CALLING_CONVENTION));
> // Binary RelNode with identical input on either side
> PhysBiRel parent = new PhysBiRel(
> cluster, cluster.traitSetOf(PHYS_CALLING_CONVENTION), singlePhy,
> singlePhy);
> planner.setRoot(parent);
> RelNode result = planner.chooseDelegate().findBestExp();
> // Expect inputs to remain identical
> assertEquals(result.getInput(0), result.getInput(1));
> } {code}
>
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