[jira] [Resolved] (CALCITE-926) Rules cannot be matched because of missing "parent link"

["Julian Hyde (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CALCITE-926?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Julian Hyde resolved CALCITE-926.
---------------------------------
    Resolution: Fixed

Fixed in http://git-wip-us.apache.org/repos/asf/incubator-calcite/commit/2c339be1. Thanks for the patch, [~maryannxue]!

> Rules cannot be matched because of missing "parent link"
> --------------------------------------------------------
>
>                 Key: CALCITE-926
>                 URL: https://issues.apache.org/jira/browse/CALCITE-926
>             Project: Calcite
>          Issue Type: Bug
>            Reporter: Maryann Xue
>            Assignee: Maryann Xue
>             Fix For: 1.5.0
>
>         Attachments: CALCITE-926.patch, CALCITE-926_2.patch
>
>
> There is no "parent link" in RelSubset, it is only for RelSet. However, RelSubset provides a "getParentRels()" link.
> {code}
>   public Collection<RelNode> getParentRels() {
>     final Set<RelNode> list = new LinkedHashSet<RelNode>();
>   parentLoop:
>     for (RelNode parent : set.getParentRels()) {
>       for (RelSubset rel : inputSubsets(parent)) {
>         if (rel.set == set && rel.getTraitSet().equals(traitSet)) {
>           list.add(parent);
>           continue parentLoop;
>         }
>       }
>     }
>     return list;
>   }
> {code}
> Now that we have a RelNode {{P1}} and its input subset is {{S1}}, and we have a rule that matches {{P1}} and does the following:
> {code}
> onMatch(RelOptRuleCall call) {
>   RelNode P1 = call.rel(0);
>   RelNode S1 = P1.getInput(0);
>   RelTraitSet t1 = S1.getTraitSet();
>   RelTraitSet t2 = t1.replace(tx);
>   RelNode S2 = convert(S1, t2);
>   RelNode P2 = P1.copy(P1.getCluster, P1.getTraitSet(), S2);
>   call.transformTo(P2);
> }
> {code}
> Note that {{t1}} is *NOT equal* to {{t2}}. So right now we have two subsets, {{S1}} and {{S2}}, in the same set; and their parents {{P1}} and {{P2}} in another set.
> {code}
> P1            P2
> |             |
> S1(t1)        S2(t2)
> {code}
> {{getParentRels(S1)}} would return {{P1}}, and {{getParentRels(S2)}} would return {{P2}}. This works fine except when {{t1}} satisfies {{t2}} (for instance, if {{tx}} is the empty collation trait) and as a result {{S2}} subsumes {{S1}}. Thus the expression {{S2 = convert(S1, t2)}} would eventually turn into {{S1}} after conversion, so {{P2}} is also a parent of {{S1}}, and {{getParentRels(S1)}} should return {{P1, P2}} instead.
> Suppose we have a second rule that should match {{P2 - R}} subsequently, {{R}} as some Rel in {{S1}}, it would NOT be fired since {{P2}} is not returned in the parent list of {{S1}}. It would not match {{R}} in {{S2}} either since it is in the form of {{P2 - AbstractConverter - R}}.



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