Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/1797#discussion_r56329514
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/plan/rules/FlinkRuleSets.scala
---
@@ -29,50 +29,45 @@ object FlinkRuleSets {
*/
val DATASET_OPT_RULES: RuleSet = RuleSets.ofList(
- // filter rules
+ // push a filter into a join
FilterJoinRule.FILTER_ON_JOIN,
+ // push filter into the children of a join
FilterJoinRule.JOIN,
- FilterMergeRule.INSTANCE,
- FilterAggregateTransposeRule.INSTANCE,
+ // push filter through an aggregation
+ FlinkFilterAggregateTransposeRule.INSTANCE,
- // push and merge projection rules
+ // aggregation and projection rules
AggregateProjectMergeRule.INSTANCE,
- ProjectMergeRule.INSTANCE,
+ AggregateProjectPullUpConstantsRule.INSTANCE,
+ // push a projection past a filter or vice versa
ProjectFilterTransposeRule.INSTANCE,
FilterProjectTransposeRule.INSTANCE,
- AggregateProjectPullUpConstantsRule.INSTANCE,
- JoinPushExpressionsRule.INSTANCE,
+ // push a projection to the children of a join
ProjectJoinTransposeRule.INSTANCE,
+ // remove identity project
ProjectRemoveRule.INSTANCE,
+ // reorder sort and projection
SortProjectTransposeRule.INSTANCE,
ProjectSortTransposeRule.INSTANCE,
- // merge and push unions rules
- // TODO: Add a rule to enforce binary unions
+ // join rules
+ JoinPushExpressionsRule.INSTANCE,
+
+ // remove union with only a single child
UnionEliminatorRule.INSTANCE,
- FlinkJoinUnionTransposeRule.LEFT_UNION,
- FlinkJoinUnionTransposeRule.RIGHT_UNION,
--- End diff --
These rules would push a join into a union. This means that a join is
executed on each input of the union and the join results are unioned
afterwards. Additional joins are likely to cause higher resource consumption.
For example if the unioned inputs are fed into the probe-side of a join, the
build side would need to be replicated.
Unless we have very good statistics and a more fine-grained cost model, I
would not try to optimize and trust the user (at least for the Table API).
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