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https://issues.apache.org/jira/browse/FLINK-3850?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15902055#comment-15902055
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ASF GitHub Bot commented on FLINK-3850:
---------------------------------------

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

    https://github.com/apache/flink/pull/3040#discussion_r104727744
  
    --- Diff: 
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/plan/nodes/dataset/DataSetJoin.scala
 ---
    @@ -199,10 +200,21 @@ class DataSetJoin(
     
         val joinOpName = s"where: ($joinConditionToString), join: 
($joinSelectionToString)"
     
    +    //consider all fields not which are not keys are forwarded
    +    val leftIndices = (0 until 
left.getRowType.getFieldCount).diff(leftKeys)
    +    val fieldsLeft = getForwardedInput(leftDataSet.getType, returnType, 
leftIndices)
    +
    +    val rightIndices = (0 until right.getRowType.getFieldCount)
    +      .diff(rightKeys)
    --- End diff --
    
    Keys can be forwarded


> Add forward field annotations to DataSet operators generated by the Table API
> -----------------------------------------------------------------------------
>
>                 Key: FLINK-3850
>                 URL: https://issues.apache.org/jira/browse/FLINK-3850
>             Project: Flink
>          Issue Type: Improvement
>          Components: Table API & SQL
>            Reporter: Fabian Hueske
>            Assignee: Nikolay Vasilishin
>
> The DataSet API features semantic annotations [1] to hint the optimizer which 
> input fields an operator copies. This information is valuable for the 
> optimizer because it can infer that certain physical properties such as 
> partitioning or sorting are not destroyed by user functions and thus generate 
> more efficient execution plans.
> The Table API is built on top of the DataSet API and generates DataSet 
> programs and code for user-defined functions. Hence, it knows exactly which 
> fields are modified and which not. We should use this information to 
> automatically generate forward field annotations and attach them to the 
> operators. This can help to significantly improve the performance of certain 
> jobs.
> [1] 
> https://ci.apache.org/projects/flink/flink-docs-release-1.0/apis/batch/index.html#semantic-annotations



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