[CALCITE-3376] VolcanoPlanner CannotPlanException: best rel is null even though there is an option with non-infinite cost

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.21.0
• Fix Version/s: 1.22.0
• Labels: pull-request-available
• Assignee: Ruben Q L
• Reporter: Ruben Q L
• Created: 27/Sep/19 07:37
• Updated: 06/Mar/20 04:35
• Resolved: 30/Oct/19 09:40

Description

The problem can be reproduced by adding this test to PlannerTest.java:

  @Test public void testCannotPlanException() throws Exception {
    RelBuilder builder = RelBuilder.create(RelBuilderTest.config().build());
    RuleSet ruleSet =
        RuleSets.ofList(
            //EnumerableRules.ENUMERABLE_JOIN_RULE, // with this rule it works!
            JoinToCorrelateRule.INSTANCE,
            EnumerableRules.ENUMERABLE_CORRELATE_RULE,
            EnumerableRules.ENUMERABLE_PROJECT_RULE,
            EnumerableRules.ENUMERABLE_FILTER_RULE,
            EnumerableRules.ENUMERABLE_SORT_RULE,
            EnumerableRules.ENUMERABLE_UNION_RULE,
            EnumerableRules.ENUMERABLE_TABLE_SCAN_RULE);

    builder
        .scan("EMP")
        .scan("EMP")
        .union(true)

        .scan("EMP")
        .scan("EMP")
        .union(true)

        .join(
            JoinRelType.INNER,
            builder.equals(
                builder.field(2, 0, "DEPTNO"),
                builder.field(2, 1, "EMPNO")));

    RelNode relNode = builder.build();
    RelOptPlanner planner = relNode.getCluster().getPlanner();
    Program program = Programs.of(ruleSet);
    RelTraitSet toTraits = relNode.getTraitSet()
        .replace(EnumerableConvention.INSTANCE);
    RelNode output = program.run(planner, relNode, toTraits,
        ImmutableList.of(), ImmutableList.of());
    String outputStr = toString(output);
  }

Running this test causes the following exception (full stack trace attached):

org.apache.calcite.plan.RelOptPlanner$CannotPlanException: There are not enough rules to produce a node with desired properties: convention=ENUMERABLE, sort=[]. All the inputs have relevant nodes, however the cost is still infinite.
Root: rel#13:Subset#2.ENUMERABLE.[]

The last part of the message (All the inputs have relevant nodes, however the cost is still infinite) seems relevant, because we can see that rel#13's best is null, and it should be rel#21 (which has a non-infinite cost):

rel#13:Subset#2.ENUMERABLE.[], best=null, importance=1.0
    rel#14:AbstractConverter.ENUMERABLE.[](input=RelSubset#12, convention=ENUMERABLE, sort=[]), rowcount=117.6, cumulative cost={inf}
    rel#21:EnumerableCorrelate.ENUMERABLE.[](left=RelSubset#19, right=RelSubset#20, correlation=$cor0, joinType=inner, requiredColumns={7}), rowcount=1.0, cumulative cost={1770.6000000000001 rows, 2466.0 cpu, 0.0 io}

Issue Links

• is related to: CALCITE-2018 Queries failed with AssertionError: rel has lower cost than best cost of subset
• links to: GitHub Pull Request #1548