[TEZ-3348] NullPointerException in Tez MROutput while trying to write using Parquet's DeprecatedParquetOutputFormat

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.9.0, 0.8.5
• Assignee: Piyush Narang
• Reporter: Piyush Narang
• Created: 13/Jul/16 23:49
• Updated: 14/Mar/17 03:49
• Resolved: 19/Jul/16 22:04

Description

Trying to run some Tez MR jobs that write out some data using Parquet to HDFS. When I try to do so, end up seeing a NPE in the Parquet code:

java.lang.NullPointerException
	at org.apache.hadoop.fs.Path.<init>(Path.java:105)
	at org.apache.hadoop.fs.Path.<init>(Path.java:94)
	at org.apache.parquet.hadoop.mapred.DeprecatedParquetOutputFormat.getDefaultWorkFile(DeprecatedParquetOutputFormat.java:69)
	at org.apache.parquet.hadoop.mapred.DeprecatedParquetOutputFormat.access$100(DeprecatedParquetOutputFormat.java:36)
	at org.apache.parquet.hadoop.mapred.DeprecatedParquetOutputFormat$RecordWriterWrapper.<init>(DeprecatedParquetOutputFormat.java:89)
	at org.apache.parquet.hadoop.mapred.DeprecatedParquetOutputFormat.getRecordWriter(DeprecatedParquetOutputFormat.java:77)
	at org.apache.tez.mapreduce.output.MROutput.initialize(MROutput.java:416)

The flow seems to be:
1) The Parquet deprecated output format class tries to read the workOutputPath - https://github.com/apache/parquet-mr/blob/master/parquet-hadoop/src/main/java/org/apache/parquet/hadoop/mapred/DeprecatedParquetOutputFormat.java#L69
2) This calls FileOutputFormat.getWorkOutputPath(...) - https://github.com/apache/hadoop/blob/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-core/src/main/java/org/apache/hadoop/mapred/FileOutputFormat.java#L229
3) That in turn tries to read the JobContext.TASK_OUTPUT_DIR ("mapreduce.task.output.dir") constant.
4) This ends up being null and in the Parquet code we end up with an NPE in the Path class.

Looking at the Tez code, we are setting the workOutputPath in the MROutput.initCommitter method - https://github.com/apache/tez/blob/master/tez-mapreduce/src/main/java/org/apache/tez/mapreduce/output/MROutput.java#L445.

This call however, is made after the call to access the workOutputPath as part of outputFormat.getRecordWriter().

I tried out a run where I moved this initCommitter call up:

else {
      oldApiTaskAttemptContext =
          new org.apache.tez.mapreduce.hadoop.mapred.TaskAttemptContextImpl(
              jobConf, taskAttemptId,
              new MRTaskReporter(getContext()));
      initCommitter(jobConf, useNewApi); // before the getRecordWriter call

      oldOutputFormat = jobConf.getOutputFormat();
      outputFormatClassName = oldOutputFormat.getClass().getName();

      FileSystem fs = FileSystem.get(jobConf);
      String finalName = getOutputName();

      oldRecordWriter =
          oldOutputFormat.getRecordWriter(
              fs, jobConf, finalName, new MRReporter(getContext().getCounters()));
    }

I tried out a run with this and it seems to succeed. If this sounds reasonable, I can cut a PR.

Issue Links

• links to: GitHub Pull Request #11