danny0405 commented on a change in pull request #13577:
URL: https://github.com/apache/flink/pull/13577#discussion_r505244379
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File path:
flink-table/flink-table-planner-blink/src/main/scala/org/apache/flink/table/planner/plan/nodes/physical/batch/BatchExecNestedLoopJoin.scala
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@@ -94,7 +94,13 @@ class BatchExecNestedLoopJoin(
(buildRowSize + BinaryRowDataSerializer.LENGTH_SIZE_IN_BYTES) *
shuffleBuildCount(mq)
val cpuCost = leftRowCnt * rightRowCnt
val costFactory = planner.getCostFactory.asInstanceOf[FlinkCostFactory]
- costFactory.makeCost(mq.getRowCount(this), cpuCost, 0, 0, memoryCost)
+ val cost = costFactory.makeCost(mq.getRowCount(this), cpuCost, 0, 0,
memoryCost)
+ if (singleRowJoin) {
+ // Make single row join more preferable than non-single row join.
+ cost.multiplyBy(0.99)
+ } else {
+ cost
+ }
Review comment:
Without this change, the single row join plan can not be picked.
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