8_streaming.md

Documentation

Spark Streaming with Cassandra

Spark Streaming extends the core API to allow high-throughput, fault-tolerant stream processing of live data streams. Data can be ingested from many sources such as Akka, Kafka, Flume, ZeroMQ, TCP sockets, etc. Results can be stored in Cassandra.

The Basic Idea

Spark Streaming

Here is a basic Spark Streaming sample which writes to the console with wordCounts.print():

Create a StreamingContext with a SparkConf configuration

    val ssc = new StreamingContext(sparkConf, Seconds(1))

Create a DStream that will connect to serverIP:serverPort

    val lines = ssc.socketTextStream(serverIP, serverPort)

Count each word in each batch

    val words = lines.flatMap(_.split(" "))
    val pairs = words.map(word => (word, 1))
    val wordCounts = pairs.reduceByKey(_ + _)

Print a few of the counts to the console. Start the computation.

    wordCounts.print()
    ssc.start()  
    ssc.awaitTermination() // Wait for the computation to terminate

Spark Streaming With Cassandra

Now let's add the Cassandra-specific functions on the StreamingContext and RDD into scope, and we simply replace the print to console with pipe the output to Cassandra:

    import com.datastax.spark.connector.streaming._
    wordCounts.saveToCassandra("streaming_test", "words")

Setting up Streaming

Follow the directions for creating a SparkConf

Create A StreamingContext

The second required parameter is the batchDuration which sets the interval streaming data will be divided into batches: Note the Spark API provides a Milliseconds, Seconds, Minutes, all of which are accepted as this Duration. This Duration is not to be confused with the scala.concurrent.duration.Duration.

    val ssc = new StreamingContext(conf, Seconds(n))

Creating A Stream

Create any of the available or custom Spark streams. The connector supports Akka Actor streams so far, but will be supporting many more in the next release. You can extend the provided import com.datastax.spark.connector.streaming.TypedStreamingActor:

Kafka Stream: creates an input stream that pulls messages from a Kafka Broker

    val stream = KafkaUtils.createStream[String, String, StringDecoder, StringDecoder](
          ssc, kafka.kafkaParams, Map(topic -> 1), StorageLevel.MEMORY_ONLY)

Actor Stream

    val stream = ssc.actorStream[String](Props[TypedStreamingActor[String]], "stream", StorageLevel.MEMORY_AND_DISK)

Enable Spark Streaming With Cassandra

Enable Cassandra-specific functions on the StreamingContext, DStream and RDD:

    import com.datastax.spark.connector.streaming._

Writing to Cassandra From A Stream

Where streaming_test is the keyspace name and words is the table name:

Saving data:

    val wc = stream.flatMap(_.split("\\s+"))
        .map(x => (x, 1))
        .reduceByKey(_ + _)
        .saveToCassandra("streaming_test", "words", SomeColumns("word", "count")) 

Start the computation:

    ssc.start()

Reading From Cassandra From The StreamingContext

    val rdd = ssc.cassandraTable("streaming_test", "key_value").select("key", "value").where("fu = ?", 3)

For a more detailed description as well as tuning writes, see Saving Data to Cassandra.

Find out more

https://spark.apache.org/docs/latest/streaming-programming-guide.html

Next - The spark-cassandra-connector-embedded Artifact