Github user tdas commented on a diff in the pull request:
https://github.com/apache/spark/pull/3798#discussion_r23726607
--- Diff:
external/kafka/src/main/scala/org/apache/spark/streaming/kafka/KafkaUtils.scala
---
@@ -144,4 +150,116 @@ object KafkaUtils {
createStream[K, V, U, T](
jssc.ssc, kafkaParams.toMap,
Map(topics.mapValues(_.intValue()).toSeq: _*), storageLevel)
}
+
+ /** A batch-oriented interface for consuming from Kafka.
+ * Starting and ending offsets are specified in advance,
+ * so that you can control exactly-once semantics.
+ * @param sc SparkContext object
+ * @param kafkaParams Kafka <a
href="http://kafka.apache.org/documentation.html#configuration";>
+ * configuration parameters</a>.
+ * Requires "metadata.broker.list" or "bootstrap.servers" to be set
with Kafka broker(s),
+ * NOT zookeeper servers, specified in host1:port1,host2:port2 form.
+ * @param batch Each OffsetRange in the batch corresponds to a
+ * range of offsets for a given Kafka topic/partition
+ * @param messageHandler function for translating each message into the
desired type
+ */
+ def createRDD[
+ K: ClassTag,
+ V: ClassTag,
+ U <: Decoder[_]: ClassTag,
+ T <: Decoder[_]: ClassTag,
+ R: ClassTag] (
+ sc: SparkContext,
+ kafkaParams: Map[String, String],
+ batch: Array[OffsetRange],
+ messageHandler: MessageAndMetadata[K, V] => R
+ ): RDD[R] = {
+ val parts = batch.zipWithIndex.map { case (o, i) =>
+ new KafkaRDDPartition(i, o.topic, o.partition, o.fromOffset,
o.untilOffset, o.host, o.port)
+ }.toArray
+ new KafkaRDD[K, V, U, T, R](sc, kafkaParams, parts, messageHandler)
+ }
+
+ /**
+ * This DOES NOT guarantee that side-effects of an action will see each
message exactly once.
--- End diff --
Docs must first start with what the operation does, not what it does not do
:) You have to first specify what the operation does (see createStream in this
class). I suggest somethig like this.
```
Create an input stream that pulls messages exactly-once from Kafka.
Compared to `createStream`, stream created by this will guarantee that each
record from Kafka is received by the application only once (despite failures,
etc.).
Note: This does not guarantee that any output operation will push each
record only once. To ensure end-to-end exactly-once semantics (that is,
receiving exactly once and outputting exactly once), you have to ensure that
the output operation is either idempotent or transactional. See the programming
guide for more details.
```
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