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From: zsxwing <git@git.apache.org>
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Subject: [GitHub] spark pull request: [SPARK-2629][STREAMING] Basic
 implementation o...
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Message-Id: <20151106004713.36775E3938@git1-us-west.apache.org>
Date: Fri,  6 Nov 2015 00:47:13 +0000 (UTC)

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

    https://github.com/apache/spark/pull/9256#discussion_r44091385
  
    --- Diff: streaming/src/main/scala/org/apache/spark/streaming/dstream/EmittedRecordsDStream.scala ---
    @@ -0,0 +1,101 @@
    +/*
    + * 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.spark.streaming.dstream
    +
    +import scala.reflect.ClassTag
    +
    +import org.apache.spark._
    +import org.apache.spark.rdd.{EmptyRDD, RDD}
    +import org.apache.spark.storage.StorageLevel
    +import org.apache.spark.streaming._
    +import org.apache.spark.streaming.rdd.{TrackStateRDD, TrackStateRDDRecord}
    +
    +
    +abstract class EmittedRecordsDStream[K: ClassTag, V: ClassTag, S: ClassTag, T: ClassTag](
    +    ssc: StreamingContext) extends DStream[T](ssc) {
    +
    +  def stateSnapshots(): DStream[(K, S)]
    +}
    +
    +
    +private[streaming] class EmittedRecordsDStreamImpl[
    +    K: ClassTag, V: ClassTag, S: ClassTag, T: ClassTag](
    +    trackStateDStream: TrackStateDStream[K, V, S, T])
    +  extends EmittedRecordsDStream[K, V, S, T](trackStateDStream.context) {
    +
    +  override def slideDuration: Duration = trackStateDStream.slideDuration
    +
    +  override def dependencies: List[DStream[_]] = List(trackStateDStream)
    +
    +  override def compute(validTime: Time): Option[RDD[T]] = {
    +    trackStateDStream.getOrCompute(validTime).map { _.flatMap[T] { _.emittedRecords } }
    +  }
    +
    +  def stateSnapshots(): DStream[(K, S)] = {
    +    trackStateDStream.flatMap[(K, S)] {
    +      _.stateMap.getAll().map { case (k, s, _) => (k, s) }.toTraversable }
    +  }
    +}
    +
    +/**
    + * A DStream that allows per-key state to be maintains, and arbitrary records to be generated
    + * based on updates to the state.
    + *
    + * @param parent Parent (key, value) stream that is the source
    + * @param spec Specifications of the trackStateByKey operation
    + * @tparam K   Key type
    + * @tparam V   Value type
    + * @tparam S   Type of the state maintained
    + * @tparam T   Type of the eiitted records
    + */
    +private[streaming] class TrackStateDStream[K: ClassTag, V: ClassTag, S: ClassTag, T: ClassTag](
    +    parent: DStream[(K, V)], spec: TrackStateSpecImpl[K, V, S, T])
    +  extends DStream[TrackStateRDDRecord[K, S, T]](parent.context) {
    +
    +  persist(StorageLevel.MEMORY_ONLY)
    +
    +  private val partitioner = spec.getPartitioner().getOrElse(
    +    new HashPartitioner(ssc.sc.defaultParallelism))
    +
    +  private val trackingFunction = spec.getFunction()
    +
    +  override def slideDuration: Duration = parent.slideDuration
    +
    +  override def dependencies: List[DStream[_]] = List(parent)
    +
    +  override val mustCheckpoint = true
    +
    +  /** Method that generates a RDD for the given time */
    +  override def compute(validTime: Time): Option[RDD[TrackStateRDDRecord[K, S, T]]] = {
    +    val prevStateRDD = getOrCompute(validTime - slideDuration).getOrElse {
    +      TrackStateRDD.createFromPairRDD[K, V, S, T](
    +        spec.getInitialStateRDD().getOrElse(new EmptyRDD[(K, S)](ssc.sparkContext)),
    +        partitioner,
    +        validTime.milliseconds
    +      )
    +    }
    +    val newDataRDD = parent.getOrCompute(validTime).get
    --- End diff --
    
    `parent.getOrCompute(validTime)` could return `None`


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