Same DAG Log Is Recorded Twice for a Streaming Task

Question

I use Spark Streaming to run the following command:

spark-submit -master yarn-client --conf spark.logLineage=true --jars $SPARK_HOME/jars/streamingClient/kafka-clients-0.8.2.1.jar,$SPARK_HOME/jars/streamingClient/kafka_2.11-0.8.2.1.jar,$SPARK_HOME/jars/streamingClient/spark-streaming-kafka-0-8_2.11-2.1.0.jar --class com.huaweixxx.bigdata.spark.examples.FemaleInfoCollectionPrint /opt/female/SparkStreamingJavaExample-1.0.jar <checkpoint> <batchTime> <windowTime> <topics> <brokers>

When there is no Kafka data input, the directed acyclic graph (DAG) of RDD displayed in the log is printed twice in a batch. The log is as follows:

-------------------------------------------
Time: 1491447950000 ms

-------------------------------------------

17/04/06 11:06:00 INFO SparkContext: RDD's recursive dependencies:  
(2) MapPartitionsRDD[49] at filter at FemaleInfoCollectionPrint.java:111 []
   |  MapPartitionsRDD[48] at reduceByKeyAndWindow at FemaleInfoCollectionPrint.java:98 []
   |  CoGroupedRDD[47] at reduceByKeyAndWindow at FemaleInfoCollectionPrint.java:98 []
   |  MapPartitionsRDD[38] at reduceByKeyAndWindow at FemaleInfoCollectionPrint.java:98 []
   |      CachedPartitions: 2; MemorySize: 8.0 B; ExternalBlockStoreSize: 0.0 B; DiskSize: 0.0 B
   |  ReliableCheckpointRDD[40] at print at FemaleInfoCollectionPrint.java:123 []
   |  ShuffledRDD[36] at reduceByKeyAndWindow at FemaleInfoCollectionPrint.java:98 []
   |      CachedPartitions: 2; MemorySize: 8.0 B; ExternalBlockStoreSize: 0.0 B; DiskSize: 0.0 B
   +-(5) MapPartitionsRDD[35] at map at FemaleInfoCollectionPrint.java:81 []
      |  MapPartitionsRDD[34] at filter at FemaleInfoCollectionPrint.java:81 []
      |  MapPartitionsRDD[33] at map at FemaleInfoCollectionPrint.java:72 []
      |  MapPartitionsRDD[32] at map at FemaleInfoCollectionPrint.java:63 []
      |  KafkaRDD[31] at createDirectStream at FemaleInfoCollectionPrint.java:63 []
   |  ShuffledRDD[46] at reduceByKeyAndWindow at FemaleInfoCollectionPrint.java:98 []
   +-(5) MapPartitionsRDD[45] at map at FemaleInfoCollectionPrint.java:81 []
      |  MapPartitionsRDD[44] at filter at FemaleInfoCollectionPrint.java:81 []
      |  MapPartitionsRDD[43] at map at FemaleInfoCollectionPrint.java:72 []
      |  MapPartitionsRDD[42] at map at FemaleInfoCollectionPrint.java:63 []
  |  KafkaRDD[41] at createDirectStream at FemaleInfoCollectionPrint.java:63 []

17/04/06 11:06:00 INFO SparkContext: RDD's recursive dependencies:  (2) MapPartitionsRDD[48] at reduceByKeyAndWindow at FemaleInfoCollectionPrint.java:98 [Memory Serialized 1x Replicated]
   |       CachedPartitions: 1; MemorySize: 4.0 B; ExternalBlockStoreSize: 0.0 B; DiskSize: 0.0 B
   |  CoGroupedRDD[47] at reduceByKeyAndWindow at FemaleInfoCollectionPrint.java:98 [Memory Serialized 1x Replicated]
   |  MapPartitionsRDD[38] at reduceByKeyAndWindow at FemaleInfoCollectionPrint.java:98 [Memory Serialized 1x Replicated]
   |      CachedPartitions: 2; MemorySize: 8.0 B; ExternalBlockStoreSize: 0.0 B; DiskSize: 0.0 B
   |  ReliableCheckpointRDD[40] at print at FemaleInfoCollectionPrint.java:123 [Memory Serialized 1x Replicated]
   |  ShuffledRDD[36] at reduceByKeyAndWindow at FemaleInfoCollectionPrint.java:98 [Memory Serialized 1x Replicated]
   |      CachedPartitions: 2; MemorySize: 8.0 B; ExternalBlockStoreSize: 0.0 B; DiskSize: 0.0 B
   +-(5) MapPartitionsRDD[35] at map at FemaleInfoCollectionPrint.java:81 [Memory Serialized 1x Replicated]
      |  MapPartitionsRDD[34] at filter at FemaleInfoCollectionPrint.java:81 [Memory Serialized 1x Replicated]
      |  MapPartitionsRDD[33] at map at FemaleInfoCollectionPrint.java:72 [Memory Serialized 1x Replicated]
      |  MapPartitionsRDD[32] at map at FemaleInfoCollectionPrint.java:63 [Memory Serialized 1x Replicated]
      |  KafkaRDD[31] at createDirectStream at FemaleInfoCollectionPrint.java:63 [Memory Serialized 1x Replicated]
   |  ShuffledRDD[46] at reduceByKeyAndWindow at FemaleInfoCollectionPrint.java:98 [Memory Serialized 1x Replicated]
   |      CachedPartitions: 1; MemorySize: 4.0 B; ExternalBlockStoreSize: 0.0 B; DiskSize: 0.0 B
   +-(5) MapPartitionsRDD[45] at map at FemaleInfoCollectionPrint.java:81 [Memory Serialized 1x Replicated]
      |  MapPartitionsRDD[44] at filter at FemaleInfoCollectionPrint.java:81 [Memory Serialized 1x Replicated]
      |  MapPartitionsRDD[43] at map at FemaleInfoCollectionPrint.java:72 [Memory Serialized 1x Replicated]
      |  MapPartitionsRDD[42] at map at FemaleInfoCollectionPrint.java:63 [Memory Serialized 1x Replicated]
  |  KafkaRDD[41] at createDirectStream at FemaleInfoCollectionPrint.java:63 [Memory Serialized 1x Replicated]

-------------------------------------------
Time: 1491447960000 ms
-------------------------------------------

Answer

In this program, the print operator in DStream is used to display the result. This operator calls the take operator in RDD to implement bottom-layer calculation.

The take operator triggers calculation for multiple times by partition.

In this problem, due to the shuffle operation, the take operator has two partitions by default. Spark Streaming first calculates the first partition. But because there is no data input, the number of obtained results is less than 10. Then the second calculation is triggered. Therefore, the DAG of RDD is printed twice.

To resolve this issue, change the print operator to foreach(collect) in the code.