Apache Spark: saveAsTextFile not working correctly in Stand Alone Mode

Question

I wrote a simple Apache Spark (1.2.0) Java program to import a text file and then write it to disk using saveAsTextFile. But the output folder either has no content (just the _SUCCESS file) or at times has incomplete data (data from just 1/2 of the tasks ).

When I do a rdd.count() on the RDD, it shows the correct number, so I know the RDD correctly constructed, it is just the saveAsTextFile method which is not working.

Here is the code:

/* SimpleApp.java */
import java.util.List;

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 = "/tmp/READ_ME.txt"; // Should be some file on your system
       SparkConf conf = new SparkConf().setAppName("Simple Application");
       JavaSparkContext sc = new JavaSparkContext(conf);
       JavaRDD<String> logData = sc.textFile(logFile);

       logData.saveAsTextFile("/tmp/simple-output");
       System.out.println("Lines -> " + logData.count());
    }
  }

Answer 1

This is because you're saving to a local path. Are you running multiple machines? so, each worker is saving to its own /tmp directory. Sometimes, you have the driver executing a task so you get part of the result locally. Really you won't want to mix distributed mode and local file systems.