spark-instrumented-optimizer/docs/quick-start.md

layout	title
global	Quick Start

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This tutorial provides a quick introduction to using Spark. We will first introduce the API through Spark's interactive Scala shell (don't worry if you don't know Scala -- you will not need much for this), then show how to write standalone applications in Scala, Java, and Python. See the programming guide for a more complete reference.

To follow along with this guide, you only need to have successfully built Spark on one machine. Simply go into your Spark directory and run:

{% highlight bash %} $ sbt/sbt assembly {% endhighlight %}

Interactive Analysis with the Spark Shell

Basics

Spark's interactive shell provides a simple way to learn the API, as well as a powerful tool to analyze datasets interactively. Start the shell by running ./bin/spark-shell in the Spark directory.

Spark's primary abstraction is a distributed collection of items called a Resilient Distributed Dataset (RDD). RDDs can be created from Hadoop InputFormats (such as HDFS files) or by transforming other RDDs. Let's make a new RDD from the text of the README file in the Spark source directory:

{% highlight scala %} scala> val textFile = sc.textFile("README.md") textFile: spark.RDD[String] = spark.MappedRDD@2ee9b6e3 {% endhighlight %}

RDDs have actions, which return values, and transformations, which return pointers to new RDDs. Let's start with a few actions:

{% highlight scala %} scala> textFile.count() // Number of items in this RDD res0: Long = 74

scala> textFile.first() // First item in this RDD res1: String = # Apache Spark {% endhighlight %}

Now let's use a transformation. We will use the filter transformation to return a new RDD with a subset of the items in the file.

{% highlight scala %} scala> val linesWithSpark = textFile.filter(line => line.contains("Spark")) linesWithSpark: spark.RDD[String] = spark.FilteredRDD@7dd4af09 {% endhighlight %}

We can chain together transformations and actions:

{% highlight scala %} scala> textFile.filter(line => line.contains("Spark")).count() // How many lines contain "Spark"? res3: Long = 15 {% endhighlight %}

More on RDD Operations

RDD actions and transformations can be used for more complex computations. Let's say we want to find the line with the most words:

{% highlight scala %} scala> textFile.map(line => line.split(" ").size).reduce((a, b) => if (a > b) a else b) res4: Long = 16 {% endhighlight %}

This first maps a line to an integer value, creating a new RDD. reduce is called on that RDD to find the largest line count. The arguments to map and reduce are Scala function literals (closures), and can use any language feature or Scala/Java library. For example, we can easily call functions declared elsewhere. We'll use Math.max() function to make this code easier to understand:

{% highlight scala %} scala> import java.lang.Math import java.lang.Math

scala> textFile.map(line => line.split(" ").size).reduce((a, b) => Math.max(a, b)) res5: Int = 16 {% endhighlight %}

One common data flow pattern is MapReduce, as popularized by Hadoop. Spark can implement MapReduce flows easily:

{% highlight scala %} scala> val wordCounts = textFile.flatMap(line => line.split(" ")).map(word => (word, 1)).reduceByKey((a, b) => a + b) wordCounts: spark.RDD[(java.lang.String, Int)] = spark.ShuffledAggregatedRDD@71f027b8 {% endhighlight %}

Here, we combined the flatMap, map and reduceByKey transformations to compute the per-word counts in the file as an RDD of (String, Int) pairs. To collect the word counts in our shell, we can use the collect action:

{% highlight scala %} scala> wordCounts.collect() res6: Array[(java.lang.String, Int)] = Array((need,2), ("",43), (Extra,3), (using,1), (passed,1), (etc.,1), (its,1), (/usr/local/lib/libmesos.so,1), (SCALA_HOME,1), (option,1), (these,1), (#,1), (PATH,,2), (200,1), (To,3),... {% endhighlight %}

Caching

Spark also supports pulling data sets into a cluster-wide in-memory cache. This is very useful when data is accessed repeatedly, such as when querying a small "hot" dataset or when running an iterative algorithm like PageRank. As a simple example, let's mark our linesWithSpark dataset to be cached:

{% highlight scala %} scala> linesWithSpark.cache() res7: spark.RDD[String] = spark.FilteredRDD@17e51082

scala> linesWithSpark.count() res8: Long = 15

scala> linesWithSpark.count() res9: Long = 15 {% endhighlight %}

It may seem silly to use Spark to explore and cache a 30-line text file. The interesting part is that these same functions can be used on very large data sets, even when they are striped across tens or hundreds of nodes. You can also do this interactively by connecting bin/spark-shell to a cluster, as described in the programming guide.

A Standalone Application

Now say we wanted to write a standalone application using the Spark API. We will walk through a simple application in both Scala (with SBT), Java (with Maven), and Python.

We'll create a very simple Spark application in Scala. So simple, in fact, that it's named SimpleApp.scala:

{% highlight scala %} /*** SimpleApp.scala ***/ import org.apache.spark.SparkContext import org.apache.spark.SparkContext._ import org.apache.spark.SparkConf

object SimpleApp { def main(args: Array[String]) { val logFile = "YOUR_SPARK_HOME/README.md" // Should be some file on your system val conf = new SparkConf().setAppName("Simple Application") val sc = new SparkContext(conf) val logData = sc.textFile(logFile, 2).cache() val numAs = logData.filter(line => line.contains("a")).count() val numBs = logData.filter(line => line.contains("b")).count() println("Lines with a: %s, Lines with b: %s".format(numAs, numBs)) } } {% endhighlight %}

This program just counts the number of lines containing 'a' and the number containing 'b' in the Spark README. Note that you'll need to replace YOUR_SPARK_HOME with the location where Spark is installed. Unlike the earlier examples with the Spark shell, which initializes its own SparkContext, we initialize a SparkContext as part of the program.

We pass the SparkContext constructor a SparkConf object which contains information about our application. We also call sc.addJar to make sure that when our application is launched in cluster mode, the jar file containing it will be shipped automatically to worker nodes.

This file depends on the Spark API, so we'll also include an sbt configuration file, simple.sbt which explains that Spark is a dependency. This file also adds a repository that Spark depends on:

{% highlight scala %} name := "Simple Project"

version := "1.0"

scalaVersion := "{{site.SCALA_VERSION}}"

libraryDependencies += "org.apache.spark" %% "spark-core" % "{{site.SPARK_VERSION}}"

resolvers += "Akka Repository" at "http://repo.akka.io/releases/" {% endhighlight %}

For sbt to work correctly, we'll need to layout SimpleApp.scala and simple.sbt according to the typical directory structure. Once that is in place, we can create a JAR package containing the application's code, then use the spark-submit script to run our program.

{% highlight bash %}

Your directory layout should look like this

$ find . . ./simple.sbt ./src ./src/main ./src/main/scala ./src/main/scala/SimpleApp.scala

Package a jar containing your application

$ sbt package ... [info] Packaging {..}/{..}/target/scala-2.10/simple-project_2.10-1.0.jar

Use spark-submit to run your application

$ YOUR_SPARK_HOME/bin/spark-submit target/scala-2.10/simple-project_2.10-1.0.jar
--class "SimpleApp"
--master local[4] ... Lines with a: 46, Lines with b: 23 {% endhighlight %}

This example will use Maven to compile an application jar, but any similar build system will work.

We'll create a very simple Spark application, SimpleApp.java:

{% highlight java %} /*** SimpleApp.java **/ import org.apache.spark.api.java.; import org.apache.spark.SparkConf; import org.apache.spark.api.java.function.Function;

public class SimpleApp { public static void main(String[] args) { String logFile = "YOUR_SPARK_HOME/README.md"; // Should be some file on your system SparkConf conf = new SparkConf().setAppName("Simple Application"); JavaSparkContext sc = new JavaSparkContext(conf); JavaRDD logData = sc.textFile(logFile).cache();

long numAs = logData.filter(new Function<String, Boolean>() {
  public Boolean call(String s) { return s.contains("a"); }
}).count();

long numBs = logData.filter(new Function<String, Boolean>() {
  public Boolean call(String s) { return s.contains("b"); }
}).count();

System.out.println("Lines with a: " + numAs + ", lines with b: " + numBs);

} } {% endhighlight %}

This program just counts the number of lines containing 'a' and the number containing 'b' in a text file. Note that you'll need to replace YOUR_SPARK_HOME with the location where Spark is installed. As with the Scala example, we initialize a SparkContext, though we use the special JavaSparkContext class to get a Java-friendly one. We also create RDDs (represented by JavaRDD) and run transformations on them. Finally, we pass functions to Spark by creating classes that extend spark.api.java.function.Function. The Java programming guide describes these differences in more detail.

To build the program, we also write a Maven pom.xml file that lists Spark as a dependency. Note that Spark artifacts are tagged with a Scala version.

{% highlight xml %} edu.berkeley simple-project 4.0.0 Simple Project jar 1.0 Akka repository http://repo.akka.io/releases org.apache.spark spark-core_{{site.SCALA_BINARY_VERSION}} {{site.SPARK_VERSION}} {% endhighlight %}

We lay out these files according to the canonical Maven directory structure: {% highlight bash %} $ find . ./pom.xml ./src ./src/main ./src/main/java ./src/main/java/SimpleApp.java {% endhighlight %}

Now, we can package the application using Maven and execute it with ./bin/spark-submit.

{% highlight bash %}

Package a jar containing your application

$ mvn package ... [INFO] Building jar: {..}/{..}/target/simple-project-1.0.jar

Use spark-submit to run your application

$ YOUR_SPARK_HOME/bin/spark-submit target/simple-project-1.0.jar
--class "SimpleApp"
--master local[4] ... Lines with a: 46, Lines with b: 23 {% endhighlight %}

Now we will show how to write a standalone application using the Python API (PySpark).

As an example, we'll create a simple Spark application, SimpleApp.py:

{% highlight python %} """SimpleApp.py""" from pyspark import SparkContext

logFile = "YOUR_SPARK_HOME/README.md" # Should be some file on your system sc = SparkContext("local", "Simple App") logData = sc.textFile(logFile).cache()

numAs = logData.filter(lambda s: 'a' in s).count() numBs = logData.filter(lambda s: 'b' in s).count()

print "Lines with a: %i, lines with b: %i" % (numAs, numBs) {% endhighlight %}

This program just counts the number of lines containing 'a' and the number containing 'b' in a text file. Note that you'll need to replace YOUR_SPARK_HOME with the location where Spark is installed. As with the Scala and Java examples, we use a SparkContext to create RDDs. We can pass Python functions to Spark, which are automatically serialized along with any variables that they reference. For applications that use custom classes or third-party libraries, we can add those code dependencies to SparkContext to ensure that they will be available on remote machines; this is described in more detail in the Python programming guide. SimpleApp is simple enough that we do not need to specify any code dependencies.

We can run this application using the bin/pyspark script:

{% highlight python %} $ cd $SPARK_HOME $ ./bin/pyspark SimpleApp.py ... Lines with a: 46, Lines with b: 23 {% endhighlight python %}

Where to go from here

Congratulations on running your first Spark application!

• For an in-depth overview of the API see "Programming Guides" menu section.
• For running applications on a cluster head to the deployment overview.
• For configuration options available to Spark applications see the configuration page.