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From fhueske <...@git.apache.org>
Subject [GitHub] flink pull request #3364: [FLINK-5047] [table] Add sliding group-windows for...
Date Tue, 07 Mar 2017 17:23:17 GMT
Github user fhueske commented on a diff in the pull request:

    https://github.com/apache/flink/pull/3364#discussion_r104726234
  
    --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/runtime/aggregate/DataSetSlideWindowAggReduceCombineFunction.scala
---
    @@ -0,0 +1,88 @@
    +/*
    + * Licensed to the Apache Software Foundation (ASF) under one
    + * or more contributor license agreements.  See the NOTICE file
    + * distributed with this work for additional information
    + * regarding copyright ownership.  The ASF licenses this file
    + * to you under the Apache License, Version 2.0 (the
    + * "License"); you may not use this file except in compliance
    + * with the License.  You may obtain a copy of the License at
    + *
    + *     http://www.apache.org/licenses/LICENSE-2.0
    + *
    + * Unless required by applicable law or agreed to in writing, software
    + * distributed under the License is distributed on an "AS IS" BASIS,
    + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    + * See the License for the specific language governing permissions and
    + * limitations under the License.
    + */
    +package org.apache.flink.table.runtime.aggregate
    +
    +import java.lang.Iterable
    +
    +import org.apache.flink.api.common.functions.CombineFunction
    +import org.apache.flink.types.Row
    +
    +/**
    +  * Wraps the aggregate logic inside of
    +  * [[org.apache.flink.api.java.operators.GroupReduceOperator]] and
    +  * [[org.apache.flink.api.java.operators.GroupCombineOperator]].
    +  *
    +  * It is used for sliding on batch for both time and count-windows.
    +  *
    +  * @param aggregates aggregate functions.
    +  * @param groupKeysMapping index mapping of group keys between intermediate aggregate
Row
    +  *                         and output Row.
    +  * @param aggregateMapping index mapping between aggregate function list and aggregated
value
    +  *                         index in output Row.
    +  * @param intermediateRowArity intermediate row field count
    +  * @param finalRowArity output row field count
    +  * @param finalRowWindowStartPos relative window-start position to last field of output
row
    +  * @param finalRowWindowEndPos relative window-end position to last field of output
row
    +  * @param windowSize size of the window, used to determine window-end for output row
    +  */
    +class DataSetSlideWindowAggReduceCombineFunction(
    +    aggregates: Array[Aggregate[_ <: Any]],
    +    groupKeysMapping: Array[(Int, Int)],
    +    aggregateMapping: Array[(Int, Int)],
    +    intermediateRowArity: Int,
    +    finalRowArity: Int,
    +    finalRowWindowStartPos: Option[Int],
    +    finalRowWindowEndPos: Option[Int],
    +    windowSize: Long)
    +  extends DataSetSlideWindowAggReduceGroupFunction(
    +    aggregates,
    +    groupKeysMapping,
    +    aggregateMapping,
    +    intermediateRowArity,
    +    finalRowArity,
    +    finalRowWindowStartPos,
    +    finalRowWindowEndPos,
    +    windowSize)
    +  with CombineFunction[Row, Row] {
    +
    +  override def combine(records: Iterable[Row]): Row = {
    +    // initiate intermediate aggregate value
    +    aggregates.foreach(_.initiate(aggregateBuffer))
    +
    +    val iterator = records.iterator()
    +    while (iterator.hasNext) {
    +      val record = iterator.next()
    +      aggregates.foreach(_.merge(record, aggregateBuffer))
    +
    +      // check if this record is the last record
    +      if (!iterator.hasNext) {
    +        // set group keys to aggregateBuffer
    +        for (i <- groupKeysMapping.indices) {
    +          aggregateBuffer.setField(i, record.getField(i))
    +        }
    +
    +        aggregateBuffer.setField(windowStartFieldPos, record.getField(windowStartFieldPos))
    +
    +        return aggregateBuffer
    +      }
    +    }
    +
    +    // this code path should never be reached as we return before the loop finishes
    +    throw new IllegalArgumentException("Group is empty. This should never happen.")
    --- End diff --
    
    OK, but how about we make that more clear with a comment like:
    
    `// This will never happen because the iterator is never null but we have to satisfy the
compiler.`


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