Richard Searle


Spark SQL against streaming data in memory

19 Jan 2015

Slides 67 to 73 from this presentation provide a simple Spark streaming application that uses Spark SQL to process the data.

A little effort is required to make this into a functional program for Spark 1.2

import org.apache.spark.streaming._
import org.apache.spark.sql._
import org.apache.spark._

object Experiment extends App {
  val conf = new SparkConf()
    .set("spark.executor.memory", "1g")
    .set("spark.cleaner.ttl", "30")
    .set("spark.streaming.receiver.maxRate", "400000")

  val sparkContext = new SparkContext(conf)
  val streamingContext = new StreamingContext(sparkContext, Seconds(10))
  val sqlContext = new SQLContext(sparkContext)
  import sqlContext._

  case class Flight(
    number: Int,
    carrier: String,
    origin: String,
    destination: String)

  object FlightParser {
    def parse(str: String): List[Flight] =
      str.split(" ").grouped(4).
        collect { case Array(n, c, o, d) => Flight(n.toInt, c, o, d) }.toList

  val server = "localhost"
  var port = 12345

  val dStream = streamingContext.socketTextStream(server,
    port, StorageLevel.MEMORY_ONLY)

  val flights = for {
    line <- dStream
    flight <- FlightParser.parse(line)
  } yield flight

  flights.foreachRDD { (rdd, time) =>
   SELECT $time, carrier, origin, destination, COUNT(*) AS c
   FROM flights
   GROUP BY carrier,origin,destination
   LIMIT 20""").foreach(println)


Note that application will not run in Eclipse and must be forked when run from SBT, due to this issue.

The code was tested by running yes 12 a b c 13 x y z |nc -kl 12345 in another console.

This code added the following parameters so as avoid disk I/O and overflow of both disk and memory space.

  1. StorageLevel.MEMORY_ONLY
  2. set(“spark.executor.memory”, “1g”)
  3. set(“spark.cleaner.ttl”, “30”)
  4. set(“spark.streaming.receiver.maxRate”, “400000”)

The maxRate parameter is unfortunately needed since Spark does not implement the necessary flow control. That value was empirically derived so as to achieve ~97% CPU load across all 6 cores of an AMD Phenom II X6 1100T.

The web UI indicates a median rate of 400K records/second but the output indicates 800K record/second. In other words, the rate is number of lines read from the socket, rather than the number of object written into the DStream.

[info] [1421724610000,x,y,z,4000125]
[info] [1421724610000,a,b,c,4000125]