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From gallenvara <...@git.apache.org>
Subject [GitHub] flink pull request #2282: [FLINK-3940] [table] Add support for ORDER BY OFFS...
Date Wed, 03 Aug 2016 02:39:16 GMT
Github user gallenvara commented on a diff in the pull request:

    https://github.com/apache/flink/pull/2282#discussion_r73272805
  
    --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/plan/nodes/dataset/DataSetSort.scala
---
    @@ -71,11 +78,57 @@ class DataSetSort(
           partitionedDs = partitionedDs.sortPartition(fieldCollation._1, fieldCollation._2)
         }
     
    +    val offsetAndFetchDS = if (offset != null) {
    +      val offsetIndex = RexLiteral.intValue(offset)
    +      val fetchIndex = if (fetch != null) {
    +        RexLiteral.intValue(fetch) + offsetIndex
    +      } else {
    +        Int.MaxValue
    +      }
    +      if (currentParallelism != 1) {
    +        val partitionCount = partitionedDs.mapPartition(
    +          new MapPartitionFunction[Any, Int] {
    +            override def mapPartition(value: lang.Iterable[Any], out: Collector[Int]):
Unit = {
    +              val iterator = value.iterator()
    +              var elementCount = 0
    +              while (iterator.hasNext) {
    +                elementCount += 1
    +                iterator -> iterator.next()
    +              }
    +              out.collect(elementCount)
    +            }
    +          }).collect().asScala
    --- End diff --
    
    For the case where parallelism != 1, we use range partition and sort partition to get
the global order. The number of elements in every partition(range) is not always same, so
counting in partition is necessary here, IMO.


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