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https://issues.apache.org/jira/browse/CALCITE-2223?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16431471#comment-16431471
 ] 

Julian Hyde commented on CALCITE-2223:
--------------------------------------

I don't think setting importance=0 is a good solution either.

> ProjectMergeRule is infinitely matched when is applied after 
> ProjectReduceExpressionsRule
> -----------------------------------------------------------------------------------------
>
>                 Key: CALCITE-2223
>                 URL: https://issues.apache.org/jira/browse/CALCITE-2223
>             Project: Calcite
>          Issue Type: Bug
>            Reporter: Volodymyr Vysotskyi
>            Assignee: Julian Hyde
>            Priority: Critical
>
> For queries like this:
> {code:sql}
> select t1.f from (select cast(f as int) f, f from (select cast(f as int) f 
> from (values('1')) t(f))) as t1
> {code}
> OOM is thrown when {{ProjectMergeRule}} is applied before applying 
> {{ProjectReduceExpressionsRule}} in VolcanoPlanner.
>  A simple test to reproduce this issue (in {{RelOptRulesTest}}):
> {code:java}
>   @Test public void testOomProjectMergeRule() {
>     RelBuilder relBuilder = 
> RelBuilder.create(RelBuilderTest.config().build());
>     RelNode relNode = relBuilder
>         .values(new String[]{"f"}, "1")
>         .project(
>             relBuilder.alias(
>                 relBuilder.cast(relBuilder.field(0), SqlTypeName.INTEGER),
>                 "f"))
>         .project(
>             relBuilder.alias(
>                 relBuilder.cast(relBuilder.field(0), SqlTypeName.INTEGER),
>                 "f0"),
>             relBuilder.alias(relBuilder.field(0), "f"))
>         .project(
>             relBuilder.alias(relBuilder.field(0), "f"))
>         .build();
>     RelOptPlanner planner = relNode.getCluster().getPlanner();
>     RuleSet ruleSet =
>         RuleSets.ofList(
>             ReduceExpressionsRule.PROJECT_INSTANCE,
>             new ProjectMergeRuleWithLongerName(),
>             EnumerableRules.ENUMERABLE_PROJECT_RULE,
>             EnumerableRules.ENUMERABLE_VALUES_RULE);
>     Program program = Programs.of(ruleSet);
>     RelTraitSet toTraits =
>         relNode.getCluster().traitSet()
>             .replace(0, EnumerableConvention.INSTANCE);
>     RelNode output = program.run(planner, relNode, toTraits,
>         ImmutableList.<RelOptMaterialization>of(), 
> ImmutableList.<RelOptLattice>of());
>     // check for output
>   }
>   /**
>    * ProjectMergeRule inheritor which has
>    * class name greater than ProjectReduceExpressionsRule class name 
> (String.compareTo()).
>    *
>    * It is needed for RuleQueue.popMatch() method
>    * to apply this rule before ProjectReduceExpressionsRule.
>    */
>   private static class ProjectMergeRuleWithLongerName extends 
> ProjectMergeRule {
>     public ProjectMergeRuleWithLongerName() {
>       super(true, RelFactories.LOGICAL_BUILDER);
>     }
>   }
> {code}



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