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From "Ryan Blue (JIRA)" <j...@apache.org>
Subject [jira] [Created] (SPARK-26873) FileFormatWriter creates inconsistent MR job IDs
Date Wed, 13 Feb 2019 21:48:00 GMT
Ryan Blue created SPARK-26873:
---------------------------------

             Summary: FileFormatWriter creates inconsistent MR job IDs
                 Key: SPARK-26873
                 URL: https://issues.apache.org/jira/browse/SPARK-26873
             Project: Spark
          Issue Type: Bug
          Components: SQL
    Affects Versions: 2.4.0, 2.3.2, 2.2.3
            Reporter: Ryan Blue


FileFormatWriter uses the current time to create a Job ID that is used when calling Hadoop
committers. This ID is used to produce task and task attempt IDs used in commits.

The problem is that Spark [generates this Job ID|https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/FileFormatWriter.scala#L209]
in {{executeTask}} for every task:
{code:lang=scala}
  /** Writes data out in a single Spark task. */
  private def executeTask(
      description: WriteJobDescription,
      sparkStageId: Int,
      sparkPartitionId: Int,
      sparkAttemptNumber: Int,
      committer: FileCommitProtocol,
      iterator: Iterator[InternalRow]): WriteTaskResult = {

    val jobId = SparkHadoopWriterUtils.createJobID(new Date, sparkStageId)
    val taskId = new TaskID(jobId, TaskType.MAP, sparkPartitionId)
    val taskAttemptId = new TaskAttemptID(taskId, sparkAttemptNumber)

...
{code}

Because this is called in each task, the Job ID used is not consistent across tasks, which
violates the contract expected by Hadoop committers.

If a committer expects identical task IDs across attempts for correctness, this breaks correctness.
For example, a Hadoop committer should be able to rename an output file to a path based on
the task ID to ensure that only one copy is committed.

We hit this issue when preemption caused a task to die just after the commit operation. The
commit coordinator authorized a second task commit because the first did not complete due
to preemption.



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