Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/3058#discussion_r95372931
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/plan/nodes/dataset/DataSetSort.scala
---
@@ -71,6 +72,21 @@ class DataSetSort(
)
}
+ override def estimateRowCount(metadata: RelMetadataQuery): Double = {
+ val inputRowCnt = metadata.getRowCount(this.getInput)
+ if (inputRowCnt == null) {
+ inputRowCnt
+ } else {
+ val rowCount = Math.max(inputRowCnt - limitStart, 0D)
--- End diff --
Returning a cardinality estimate of `0` is not a good idea because all
remaining operations might appear to have no costs at all. Rather be
conservative and return `1` which is still low but does not invalidate any
subsequent costs.
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