zabetak commented on a change in pull request #1686: [CALCITE-3630] Improve
ReduceExpressionsRule
URL: https://github.com/apache/calcite/pull/1686#discussion_r361459282
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File path:
core/src/main/java/org/apache/calcite/rel/rules/ReduceExpressionsRule.java
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@@ -270,6 +270,8 @@ private void reduceNotNullableFilter(
} else {
call.transformTo(createEmptyRelOrEquivalent(call, filter));
}
+ // New plan is absolutely better than old plan.
+ call.getPlanner().setImportance(filter, 0.0);
Review comment:
Usages of `setImportance` indeed require some care. I think, this change for
example could lead to a `CannotPlanException` that could be avoided before.
Assume that we enter the else branch and we create an empty `LogicalValues`.
Then if the rule set does not contain a `PhysicalValues` we may end-up with a
`CannotPlanException`. Without this change this wouldn't be the case since the
old plan could still be matched by other rules and create a `PhysicalFilter`
etc. I admit this is a contrived example but I wanted to highlight that setting
importance explicitly might be risky.
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