[SPARK-4964] add comments per pwendell / dibbhatt

Author: koeninger

external/kafka/src/main/scala/org/apache/spark/streaming/kafka/KafkaCluster.scala

@@ -221,6 +221,7 @@ class KafkaCluster(val kafkaParams: Map[String, String]) extends Serializable {
   // https://cwiki.apache.org/confluence/display/KAFKA/A+Guide+To+The+Kafka+Protocol#AGuideToTheKafkaProtocol-OffsetCommit/FetchAPI
   // scalastyle:on
 
+  /** Requires Kafka >= 0.8.1.1 */
   def getConsumerOffsets(
       groupId: String,
       topicAndPartitions: Set[TopicAndPartition]
@@ -232,6 +233,7 @@ class KafkaCluster(val kafkaParams: Map[String, String]) extends Serializable {
     }
   }
 
+  /** Requires Kafka >= 0.8.1.1 */
   def getConsumerOffsetMetadata(
       groupId: String,
       topicAndPartitions: Set[TopicAndPartition]
@@ -261,6 +263,7 @@ class KafkaCluster(val kafkaParams: Map[String, String]) extends Serializable {
     Left(errs)
   }
 
+  /** Requires Kafka >= 0.8.1.1 */
   def setConsumerOffsets(
       groupId: String,
       offsets: Map[TopicAndPartition, Long]
@@ -270,6 +273,7 @@ class KafkaCluster(val kafkaParams: Map[String, String]) extends Serializable {
     })
   }
 
+  /** Requires Kafka >= 0.8.1.1 */
   def setConsumerOffsetMetadata(
       groupId: String,
       metadata: Map[TopicAndPartition, OffsetMetadataAndError]

external/kafka/src/main/scala/org/apache/spark/streaming/kafka/OffsetRange.scala

@@ -42,9 +42,6 @@ final class OffsetRange private(
 }
 
 object OffsetRange {
-  private[spark]
-  type OffsetRangeTuple = (String, Int, Long, Long)
-
   def create(topic: String, partition: Int, fromOffset: Long, untilOffset: Long): OffsetRange =
     new OffsetRange(topic, partition, fromOffset, untilOffset)
 
@@ -63,6 +60,10 @@ object OffsetRange {
       untilOffset: Long): OffsetRange =
     new OffsetRange(topicAndPartition.topic, topicAndPartition.partition, fromOffset, untilOffset)
 
+  /** this is to avoid ClassNotFoundException during checkpoint restore */
+  private[spark]
+  type OffsetRangeTuple = (String, Int, Long, Long)
+
   private[streaming]
   def apply(t: OffsetRangeTuple) =
     new OffsetRange(t._1, t._2, t._3, t._4)