Maryann Xue created CALCITE-926:
-----------------------------------
Summary: 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
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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