Github user pwendell commented on a diff in the pull request:
https://github.com/apache/spark/pull/3026#discussion_r19653425
--- Diff:
streaming/src/main/scala/org/apache/spark/streaming/scheduler/ReceivedBlockTracker.scala
---
@@ -0,0 +1,207 @@
+/*
+ * 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.scheduler
+
+import java.nio.ByteBuffer
+
+import scala.collection.mutable
+import scala.language.implicitConversions
+
+import org.apache.hadoop.conf.Configuration
+import org.apache.hadoop.fs.Path
+
+import org.apache.spark.{Logging, SparkConf}
+import org.apache.spark.storage.StreamBlockId
+import org.apache.spark.streaming.Time
+import org.apache.spark.streaming.util.{Clock, WriteAheadLogManager}
+import org.apache.spark.util.Utils
+
+/** Trait representing any action done in the ReceivedBlockTracker */
+private[streaming] sealed trait ReceivedBlockTrackerAction
+
+private[streaming] case class BlockAddition(receivedBlockInfo:
ReceivedBlockInfo)
+ extends ReceivedBlockTrackerAction
+private[streaming] case class BatchAllocations(time: Time,
allocatedBlocks: AllocatedBlocks)
+ extends ReceivedBlockTrackerAction
+private[streaming] case class BatchCleanup(times: Seq[Time])
+ extends ReceivedBlockTrackerAction
+
+
+/** Class representing the blocks of all the streams allocated to a batch
*/
+case class AllocatedBlocks(streamIdToAllocatedBlocks: Map[Int,
Seq[ReceivedBlockInfo]]) {
+ def apply(streamId: Int) = streamIdToAllocatedBlocks(streamId)
+}
+
+/**
+ * Class that keep track of all the received blocks, and allocate them to
batches
+ * when required. All actions taken by this class can be saved to a write
ahead log,
+ * so that the state of the tracker (received blocks and block-to-batch
allocations)
+ * can be recovered after driver failure.
+ */
--- End diff --
It would be good to explain that as a side effect of construction this will
attempt to read any existing state in the log contained in the checkpoint
directory. Alternatively, to keep the constructor side effect free, what if the
caller explicitly called `recoverFromWriteAheadLogs` when it constructs this
(and you'd throw an error if someone called that when there were already
blocks).
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