ASF GitHub Bot commented on FLINK-3850:

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

    --- Diff: 
    @@ -129,8 +131,35 @@ class DataSetCalc(
    +    def getForwardIndices = {
    +      //get indices of all modified operands
    +      val modifiedOperands = calcProgram.
    +        getExprList
    +        .filter(_.isInstanceOf[RexCall])
    +        .flatMap(_.asInstanceOf[RexCall].operands)
    +        .map(_.asInstanceOf[RexLocalRef].getIndex)
    --- End diff --
    Shouldn't the modified fields are meaning to the input fields? So it should 
be RexInputRef?

> 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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