Github user jerryshao commented on a diff in the pull request:
https://github.com/apache/spark/pull/2991#discussion_r20215912
--- Diff:
external/kafka/src/main/scala/org/apache/spark/streaming/kafka/ReliableKafkaReceiver.scala
---
@@ -0,0 +1,251 @@
+/*
+ * 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.kafka
+
+import java.util.Properties
+import java.util.concurrent.ConcurrentHashMap
+
+import scala.collection.Map
+import scala.collection.mutable
+import scala.reflect.{classTag, ClassTag}
+
+import kafka.common.TopicAndPartition
+import kafka.consumer.{Consumer, ConsumerConfig, ConsumerConnector,
KafkaStream}
+import kafka.serializer.Decoder
+import kafka.utils.{ZkUtils, ZKGroupTopicDirs, ZKStringSerializer,
VerifiableProperties}
+import org.I0Itec.zkclient.ZkClient
+
+import org.apache.spark.{SparkEnv, Logging}
+import org.apache.spark.storage.{StreamBlockId, StorageLevel}
+import org.apache.spark.streaming.receiver.{BlockGeneratorListener,
BlockGenerator, Receiver}
+import org.apache.spark.util.Utils
+
+
+/**
+ * ReliableKafkaReceiver offers the ability to reliably store data into
BlockManager without loss.
+ * It is turned off by default and will be enabled when
+ * spark.streaming.receiver.writeAheadLog.enable is true. The difference
compared to KafkaReceiver
+ * is that this receiver manages topic-partition/offset itself and updates
the offset information
+ * after data is reliably stored as write-ahead log. Offsets will only be
updated when data is
+ * reliably stored, so the potential data loss problem of KafkaReceiver
can be eliminated.
+ *
+ * Note: ReliableKafkaReceiver will set auto.commit.enable to false to
turn off automatic offset
+ * commit mechanism in Kafka consumer. So setting this configuration
manually within kafkaParams
+ * will not take effect.
+ */
+private[streaming]
+class ReliableKafkaReceiver[
+ K: ClassTag,
+ V: ClassTag,
+ U <: Decoder[_]: ClassTag,
+ T <: Decoder[_]: ClassTag](
+ kafkaParams: Map[String, String],
+ topics: Map[String, Int],
+ storageLevel: StorageLevel)
+ extends Receiver[(K, V)](storageLevel) with Logging {
+
+ private val groupId = kafkaParams("group.id")
+
+ private val AUTO_OFFSET_COMMIT = "auto.commit.enable"
+
+ private def conf() = SparkEnv.get.conf
+
+ /** High level consumer to connect to Kafka. */
+ private var consumerConnector: ConsumerConnector = null
+
+ /** zkClient to connect to Zookeeper to commit the offsets. */
+ private var zkClient: ZkClient = null
+
+ /**
+ * A HashMap to manage the offset for each topic/partition, this HashMap
is called in
+ * synchronized block, so mutable HashMap will not meet concurrency
issue.
+ */
+ private var topicPartitionOffsetMap: mutable.HashMap[TopicAndPartition,
Long] = null
+
+ /** A concurrent HashMap to store the stream block id and related offset
snapshot. */
+ private var blockOffsetMap: ConcurrentHashMap[StreamBlockId,
Map[TopicAndPartition, Long]] = null
+
+ /**
+ * Manage the BlockGenerator in receiver itself for better managing
block store and offset
+ * commit.
+ */
+ private var blockGenerator: BlockGenerator = null
+
+ /** Kafka offsets checkpoint listener to register into BlockGenerator
for offsets checkpoint. */
+ private final class OffsetCheckpointListener extends
BlockGeneratorListener {
+
+ override def onGenerateBlock(blockId: StreamBlockId): Unit = {
+ // Get a snapshot of current offset map and store with related block
id. Since this hook
+ // function is called in synchronized block, so we can get the
snapshot without explicit lock.
+ val offsetSnapshot = topicPartitionOffsetMap.toMap
--- End diff --
Because this hook function `onGenerateBlock` is called in function
`updateCurrentBuffer`, which is synchronized with BlockGenerator object, so I
don't think we need to add another lock here. At the time `updateCurrentBuffer`
is called, because we get a lock, so there is no data will add into
BlockGenerator and insert offset into topicPartitionOffsetMap.
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