[MAPREDUCE-86] Custom FileSystem class not found during child process initialization

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Not A Problem
• Assignee: Unassigned
• Reporter: Chris Wensel
• Created: 14/Mar/08 18:55
• Updated: 07/Jul/12 16:26
• Resolved: 07/Jul/12 16:26

Description

If a custom FileSystem class is used for Reducer output, initialization of the child task fails with an uncaught ClassNotFoundException. Trace follows.

java.lang.RuntimeException: java.lang.ClassNotFoundException: cascading.tap.hadoop.S3HttpFileSystem
java.io.IOException: java.lang.RuntimeException: java.lang.ClassNotFoundException: cascading.tap.hadoop.S3HttpFileSystem
at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:607)
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:161)
at org.apache.hadoop.fs.Path.getFileSystem(Path.java:175)
at org.apache.hadoop.mapred.Task.getTaskOutputPath(Task.java:195)
at org.apache.hadoop.mapred.Task.setConf(Task.java:400)
at org.apache.hadoop.mapred.TaskInProgress.getTaskToRun(TaskInProgress.java:733)
at org.apache.hadoop.mapred.JobInProgress.obtainNewMapTask(JobInProgress.java:568)
at org.apache.hadoop.mapred.JobTracker.getNewTaskForTaskTracker(JobTracker.java:1409)
at org.apache.hadoop.mapred.JobTracker.heartbeat(JobTracker.java:1191)
at sun.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)

Task.getTaskOutputPath only attempts to force the path into a fully qualified reference. It already handles thrown IOE, and should possibly just catch Exception, or atleast explicitly catch the CNFE. On a catch, can continue to return the original Path instance passed.

Bar.java

  private Path getTaskOutputPath(JobConf conf) {
    Path p = new Path(conf.getOutputPath(), ("_" + taskId));
    try {
      FileSystem fs = p.getFileSystem(conf);
      return p.makeQualified(fs);
    } catch (IOException ie) {  // SHOULD BE BROADENED?
      LOG.warn(StringUtils.stringifyException(ie));
      return p;
    }
  }