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[SPARK-17782][STREAMING][KAFKA] eliminate race condition of poll twice #15387

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[SPARK-17782][STREAMING][KAFKA] eliminate race condition of poll twice #15387

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1fc5863
[SPARK-17782][STREAMING][KAFKA] eliminate race condition of poll bein…
koeninger Oct 7, 2016
aca55de
[SPARK-17782][STREAMING][KAFKA] whitespace fix
koeninger Oct 7, 2016
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4 changes: 4 additions & 0 deletions ...rnal/kafka-0-10/src/main/scala/org/apache/spark/streaming/kafka010/ConsumerStrategy.scala
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Expand Up @@ -104,6 +104,8 @@ private case class Subscribe[K, V](
toSeek.asScala.foreach { case (topicPartition, offset) =>
consumer.seek(topicPartition, offset)
}
// we've called poll, we must pause or next poll may consume messages and set position
consumer.pause(consumer.assignment())
}

consumer
Expand Down Expand Up @@ -154,6 +156,8 @@ private case class SubscribePattern[K, V](
toSeek.asScala.foreach { case (topicPartition, offset) =>
consumer.seek(topicPartition, offset)
}
// we've called poll, we must pause or next poll may consume messages and set position
consumer.pause(consumer.assignment())
}

consumer
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2 changes: 1 addition & 1 deletion ...fka-0-10/src/main/scala/org/apache/spark/streaming/kafka010/DirectKafkaInputDStream.scala
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Expand Up @@ -223,7 +223,7 @@ private[spark] class DirectKafkaInputDStream[K, V](

override def start(): Unit = {
val c = consumer
c.poll(0)
assert(c.poll(0).isEmpty, "Driver shouldn't consume messages; pause if you poll during setup")
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@tdas tdas Oct 7, 2016

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Is this poll(0) guaranteed to not return any record if the previous poll(0) is paused immediately? Is there a race condition possible where the first poll(0) (inside consumer strategy) manages to actually fetch records internally before it is paused, which is then returned by this poll(0) (inside DStream)?

if (currentOffsets.isEmpty) {
currentOffsets = c.assignment().asScala.map { tp =>
tp -> c.position(tp)
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