Github user tdas commented on a diff in the pull request:
https://github.com/apache/spark/pull/11863#discussion_r68549882
--- Diff:
external/kafka-0-10/src/main/scala/org/apache/spark/streaming/kafka/ConsumerStrategy.scala
---
@@ -0,0 +1,164 @@
+/*
+ * 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 => ju }
+
+import scala.collection.JavaConverters._
+import scala.reflect.ClassTag
+
+import org.apache.kafka.clients.consumer._
+import org.apache.kafka.common.TopicPartition
+
+/**
+ * Choice of how to create and configure underlying Kafka Consumers on
driver and executors.
+ * Kafka 0.10 consumers can require additional, sometimes complex, setup
after object
+ * instantiation. This interface encapsulates that process, and allows it
to be checkpointed.
+ * @tparam K type of Kafka message key
+ * @tparam V type of Kafka message value
+ */
+trait ConsumerStrategy[K, V] {
+ /**
+ * Kafka <a
href="http://kafka.apache.org/documentation.htmll#newconsumerconfigs";>
+ * configuration parameters</a> to be used on executors. Requires
"bootstrap.servers" to be set
+ * with Kafka broker(s) specified in host1:port1,host2:port2 form.
+ */
+ def executorKafkaParams: ju.Map[String, Object]
+
+ /**
+ * Must return a fully configured Kafka Consumer, including subscribed
or assigned topics.
+ * This consumer will be used on the driver to query for offsets only,
not messages.
+ * @param currentOffsets A map from TopicPartition to offset, indicating
how far the driver
+ * has successfully read. Will be empty on initial start, possibly
non-empty on restart from
+ * checkpoint.
+ * TODO: is strategy or dstream responsible for seeking on checkpoint
restart
+ */
+ def onStart(currentOffsets: Map[TopicPartition, Long]): Consumer[K, V]
+}
+
+/**
+ * Subscribe to a collection of topics.
+ * @param topics collection of topics to subscribe
+ * @param kafkaParams Kafka
+ * <a
href="http://kafka.apache.org/documentation.htmll#newconsumerconfigs";>
+ * configuration parameters</a> to be used on driver. The same parameters
will be used on executors,
+ * with minor automatic modifications applied.
+ * Requires "bootstrap.servers" to be set
+ * with Kafka broker(s) specified in host1:port1,host2:port2 form.
+ */
+case class Subscribe[K: ClassTag, V: ClassTag](
+ topics: ju.Collection[java.lang.String],
+ kafkaParams: ju.Map[String, Object]
+ ) extends ConsumerStrategy[K, V] {
+
+ def executorKafkaParams: ju.Map[String, Object] = kafkaParams
+
+ def onStart(currentOffsets: Map[TopicPartition, Long]): Consumer[K, V] =
{
+ val consumer = new KafkaConsumer[K, V](kafkaParams)
+ consumer.subscribe(topics)
+ consumer
+ }
+}
+
+object Subscribe {
+ def create[K, V](
+ keyClass: Class[K],
+ valueClass: Class[V],
+ topics: ju.Collection[java.lang.String],
+ kafkaParams: ju.Map[String, Object]
+ ): Subscribe[K, V] = {
+ implicit val keyCmt: ClassTag[K] = ClassTag(keyClass)
+ implicit val valueCmt: ClassTag[V] = ClassTag(valueClass)
+ Subscribe[K, V](topics, kafkaParams)
+ }
+}
+
+/**
+ * Assign a fixed collection of TopicPartitions
+ * @param topicPartitions collection of TopicPartitions to subscribe
+ * @param kafkaParams Kafka
+ * <a
href="http://kafka.apache.org/documentation.htmll#newconsumerconfigs";>
+ * configuration parameters</a> to be used on driver. The same parameters
will be used on executors,
+ * with minor automatic modifications applied.
+ * Requires "bootstrap.servers" to be set
+ * with Kafka broker(s) specified in host1:port1,host2:port2 form.
+ */
+case class Assign[K: ClassTag, V: ClassTag](
+ topicPartitions: ju.Collection[TopicPartition],
+ kafkaParams: ju.Map[String, Object]
+ ) extends ConsumerStrategy[K, V] {
+
+ def executorKafkaParams: ju.Map[String, Object] = kafkaParams
+
+ def onStart(currentOffsets: Map[TopicPartition, Long]): Consumer[K, V] =
{
+ val consumer = new KafkaConsumer[K, V](kafkaParams)
+ consumer.assign(topicPartitions)
+ consumer
+ }
+}
+
+object Assign {
+ def create[K, V](
+ keyClass: Class[K],
+ valueClass: Class[V],
+ topicPartitions: ju.Collection[TopicPartition],
+ kafkaParams: ju.Map[String, Object]
+ ): Assign[K, V] = {
+ implicit val keyCmt: ClassTag[K] = ClassTag(keyClass)
+ implicit val valueCmt: ClassTag[V] = ClassTag(valueClass)
+ Assign[K, V](topicPartitions, kafkaParams)
+ }
+}
+
+
+/**
+ * Set offsets on initial startup only, after another strategy has
configured consumer
+ * @param offsets: offsets to begin at
+ * @param init: ConsumerStrategy responsible for instantiation and initial
config
+ */
+case class FromOffsets[K: ClassTag, V: ClassTag](
--- End diff --
This is the only one of the ConsumerStrategy that I have doubts on. I find
the usage of this
`FromOffset(offsets, Assign(....))` confusing in terms of code. So let me
ask this. In the common usecases, that these strategies are addressing, is
anybody ever going to use `FromOffsets` with anything other than Assign? If
not, then this is can be parameter in Assign, and it will be less confusing
syntax. And for those who indeed want to assign offsets with differently
initiated consumers, they can always create a custom ConsumerStrategy.
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