[GitHub] flink pull request #3860: [FLINK-6516] [table] using real row count instead ...

[fhueske <gi...@git.apache.org>]

Github user fhueske commented on a diff in the pull request:

    https://github.com/apache/flink/pull/3860#discussion_r127418874
  
    --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/plan/nodes/PhysicalTableSourceScan.scala ---
    @@ -70,4 +73,18 @@ abstract class PhysicalTableSourceScan(
     
       def copy(traitSet: RelTraitSet, tableSource: TableSource[_]): PhysicalTableSourceScan
     
    +  override def estimateRowCount(mq: RelMetadataQuery): Double = {
    +    val tableSourceTable = getTable.unwrap(classOf[TableSourceTable[_]])
    +
    +    if (tableSourceTable.getStatistic != FlinkStatistic.UNKNOWN) {
    --- End diff --
    
    Right, but in the current implementation the statistics of the `TableSourceTable` are preferred over the stats of the `TableSource` (`if (tableSourceTable.getStatistic != FlinkStatistic.UNKNOWN) { return rowcount; }`).
    
    If I see this correctly, the stats of the `TableSourceTable` are the stats in the catalog, but a `FilterableTableSource` knows if a filter has been pushed down and should have more accurate stats because it can apply the selectivity of the pushed down filter. 
    
    So in my opinion the `TableSource` statistics should be preferred over the static `TableSourceTable` stats.
    
    Is my reasoning correct or did I overlook something @godfreyhe?
    
    Thanks, Fabian


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