Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/2931#discussion_r19491638
--- Diff:
streaming/src/main/scala/org/apache/spark/streaming/rdd/HDFSBackedBlockRDD.scala
---
@@ -0,0 +1,92 @@
+/*
+ * 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.rdd
+
+import scala.reflect.ClassTag
+
+import org.apache.hadoop.conf.Configuration
+
+import org.apache.spark.rdd.BlockRDD
+import org.apache.spark.storage.{BlockId, StorageLevel}
+import org.apache.spark.streaming.util.{WriteAheadLogFileSegment,
HdfsUtils, WriteAheadLogRandomReader}
+import org.apache.spark._
+
+private[streaming]
+class HDFSBackedBlockRDDPartition(
+ val blockId: BlockId,
+ val index: Int,
+ val segment: WriteAheadLogFileSegment
+ ) extends Partition
+
+private[streaming]
+class HDFSBackedBlockRDD[T: ClassTag](
+ @transient sc: SparkContext,
+ @transient hadoopConfiguration: Configuration,
+ @transient override val blockIds: Array[BlockId],
+ @transient val segments: Array[WriteAheadLogFileSegment],
+ val storeInBlockManager: Boolean,
+ val storageLevel: StorageLevel
+ ) extends BlockRDD[T](sc, blockIds) {
+
+ require(blockIds.length == segments.length,
+ "Number of block ids must be the same as number of segments!")
+
+ // Hadoop Configuration is not serializable, so broadcast it as a
serializable.
+ val broadcastedHadoopConf = sc.broadcast(new
SerializableWritable(hadoopConfiguration))
+
+ override def getPartitions: Array[Partition] = {
+ assertValid()
+ (0 until blockIds.size).map { i =>
+ new HDFSBackedBlockRDDPartition(blockIds(i), i, segments(i))
+ }.toArray
+ }
+
+ override def compute(split: Partition, context: TaskContext):
Iterator[T] = {
+ assertValid()
+ val hadoopConf = broadcastedHadoopConf.value.value
+ val blockManager = SparkEnv.get.blockManager
+ val partition = split.asInstanceOf[HDFSBackedBlockRDDPartition]
+ val blockId = partition.blockId
+ blockManager.get(blockId) match {
+ // Data is in Block Manager, grab it from there.
+ case Some(block) =>
+ block.data.asInstanceOf[Iterator[T]]
+ // Data not found in Block Manager, grab it from HDFS
+ case None =>
+ logInfo("Reading partition data from write ahead log " +
partition.segment.path)
+ val reader = new WriteAheadLogRandomReader(partition.segment.path,
hadoopConf)
+ val dataRead = reader.read(partition.segment)
+ reader.close()
+ // Currently, we support storing the data to BM only in serialized
form and not in
+ // deserialized form
+ if (storeInBlockManager) {
+ blockManager.putBytes(blockId, dataRead, storageLevel)
+ }
+ dataRead.rewind()
+ blockManager.dataDeserialize(blockId,
dataRead).asInstanceOf[Iterator[T]]
+ }
+ }
+
+ override def getPreferredLocations(split: Partition): Seq[String] = {
+ val partition = split.asInstanceOf[HDFSBackedBlockRDDPartition]
+ val locations = getBlockIdLocations()
+ locations.getOrElse(partition.blockId,
--- End diff --
> we don't want to get the HDFS locations if we know that the
sparkPreferredLocations exists
The snippet that I listed actually implements this behavior: if
sparkPreferreredLocations is not `None`, then the `orElse` short-circuits and
never evaluates `hdfsPreferredLocations`.
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