Setting external jars to hadoop classpath

Question

I am trying to set external jars to hadoop classpath but no luck so far.

I have the following setup

$ hadoop version
Hadoop 2.0.6-alpha Subversion https://git-wip-us.apache.org/repos/asf/bigtop.git -r ca4c88898f95aaab3fd85b5e9c194ffd647c2109 Compiled by jenkins on 2013-10-31T07:55Z From source with checksum 95e88b2a9589fa69d6d5c1dbd48d4e This command was run using /usr/lib/hadoop/hadoop-common-2.0.6-alpha.jar

Classpath

$ echo $HADOOP_CLASSPATH
/home/tom/workspace/libs/opencsv-2.3.jar

I am able see the above HADOOP_CLASSPATH has been picked up by hadoop

$ hadoop classpath
/etc/hadoop/conf:/usr/lib/hadoop/lib/:/usr/lib/hadoop/.//:/home/tom/workspace/libs/opencsv-2.3.jar:/usr/lib/hadoop-hdfs/./:/usr/lib/hadoop-hdfs/lib/:/usr/lib/hadoop-hdfs/.//:/usr/lib/hadoop-yarn/lib/:/usr/lib/hadoop-yarn/.//:/usr/lib/hadoop-mapreduce/lib/:/usr/lib/hadoop-mapreduce/.//

Command

$ sudo hadoop jar FlightsByCarrier.jar FlightsByCarrier /user/root/1987.csv /user/root/result

I tried with -libjars option as well

$ sudo hadoop jar FlightsByCarrier.jar FlightsByCarrier /user/root/1987.csv /user/root/result -libjars /home/tom/workspace/libs/opencsv-2.3.jar

The stacktrace

14/11/04 16:43:23 INFO mapreduce.Job: Running job: job_1415115532989_0001 14/11/04 16:43:55 INFO mapreduce.Job: Job job_1415115532989_0001 running in uber mode : false 14/11/04 16:43:56 INFO mapreduce.Job: map 0% reduce 0% 14/11/04 16:45:27 INFO mapreduce.Job: map 50% reduce 0% 14/11/04 16:45:27 INFO mapreduce.Job: Task Id : attempt_1415115532989_0001_m_000001_0, Status : FAILED Error: java.lang.ClassNotFoundException: au.com.bytecode.opencsv.CSVParser at java.net.URLClassLoader$1.run(URLClassLoader.java:366) at java.net.URLClassLoader$1.run(URLClassLoader.java:355) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:354) at java.lang.ClassLoader.loadClass(ClassLoader.java:425) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308) at java.lang.ClassLoader.loadClass(ClassLoader.java:358) at FlightsByCarrierMapper.map(FlightsByCarrierMapper.java:19) at FlightsByCarrierMapper.map(FlightsByCarrierMapper.java:10) at org.apache.hadoop.mapreduce.Mapper.run(Mapper.java:144) at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:757) at org.apache.hadoop.mapred.MapTask.run(MapTask.java:339) at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:158) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:415) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1478) at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:153)

Any help is highly appreciated.

Answer 1

Your external jar is missing on the node running maps. You have to add it to the cache to make it available. Try :

DistributedCache.addFileToClassPath(new Path("pathToJar"), conf);

Not sure in which version DistributedCache was deprecated, but from Hadoop 2.2.0 onward you can use :

job.addFileToClassPath(new Path("pathToJar")); 

Answer 2

If you are adding the external JAR to the Hadoop classpath then its better to copy your JAR to one of the existing directories that hadoop is looking at. On the command line run the command "hadoop classpath" and then find a suitable folder and copy your jar file to that location and hadoop will pick up the dependencies from there. This wont work with CloudEra etc as you may not have read/write rights to copy files to the hadoop classpath folders.

Looks like you tried the LIBJARs option as well, did you edit your driver class to implement the TOOL interface? First make sure that you edit your driver class as shown below:

    public class myDriverClass extends Configured implements Tool {

      public static void main(String[] args) throws Exception {
         int res = ToolRunner.run(new Configuration(), new myDriverClass(), args);
         System.exit(res);
      }

      public int run(String[] args) throws Exception
      {

        // Configuration processed by ToolRunner 
        Configuration conf = getConf();
        Job job = new Job(conf, "My Job");

        ...
        ...

        return job.waitForCompletion(true) ? 0 : 1;
      }
    }

Now edit your "hadoop jar" command as shown below:

hadoop jar YourApplication.jar [myDriverClass] args -libjars path/to/jar/file

Now lets understand what happens underneath. Basically we are handling the new command line arguments by implementing the TOOL Interface. ToolRunner is used to run classes implementing Tool interface. It works in conjunction with GenericOptionsParser to parse the generic hadoop command line arguments and modifies the Configuration of the Tool.

Within our Main() we are calling ToolRunner.run(new Configuration(), new myDriverClass(), args) - this runs the given Tool by Tool.run(String[]), after parsing with the given generic arguments. It uses the given Configuration, or builds one if it's null and then sets the Tool's configuration with the possibly modified version of the conf.

Now within the run method, when we call getConf() we get the modified version of the Configuration. So make sure that you have the below line in your code. If you implement everything else and still make use of Configuration conf = new Configuration(), nothing would work.

Configuration conf = getConf();