Hadoop-如何从mapred.JobConf中提取taskId?

问题描述

是否可以从*mapred*.JobConf创建有效的*mapreduce*.TaskAttemptID?

Is it possible to create a valid *mapreduce*.TaskAttemptID from *mapred*.JobConf?

背景

我需要为ExistingFileInputFormat写一个FileInputFormatAdapter.问题是适配器需要扩展mapred.InputFormat，而现有格式扩展mapreduce.InputFormat.

I need to write a FileInputFormatAdapter for an ExistingFileInputFormat. The problem is that the Adapter needs to extend mapred.InputFormat and the Existing format extends mapreduce.InputFormat.

我需要构建一个mapreduce.TaskAttemptContextImpl，以便可以实例化ExistingRecordReader.但是，我无法创建有效的TaskId ... taskId显示为null.

I need to build a mapreduce.TaskAttemptContextImpl, so that I can instantiate the ExistingRecordReader. However, I can't create a valid TaskId...the taskId comes out as null.

所以我如何从mapred.JobConf获取taskId，jobId等.

So How can I get the taskId, jobId, etc from mapred.JobConf.

尤其是在适配器的getRecordReader中，我需要执行以下操作:

In particular in the Adapter's getRecordReader I need to do something like:

public org.apache.hadoop.mapred.RecordReader<NullWritable, MyWritable> getRecordReader(
        org.apache.hadoop.mapred.InputSplit split, JobConf job, Reporter reporter) throws IOException {

    SplitAdapter splitAdapter = (SplitAdapter) split;

    final Configuration conf = job;

    /*************************************************/
    //The problem is here, "mapred.task.id" is not in the conf
    /*************************************************/
    final TaskAttemptID taskId = TaskAttemptID.forName(conf.get("mapred.task.id"));

    final TaskAttemptContext context = new TaskAttemptContextImpl(conf, taskId);
    try {
        return new RecordReaderAdapter(new ExistingRecordReader(
                splitAdapter.getMapRedeuceSplit(),
                context));
    } catch (InterruptedException e) {
        throw new RuntimeException("Failed to create record-reader.", e);
    }
}

此代码引发异常:

Caused by: java.lang.NullPointerException
    at org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl.<init>(TaskAttemptContextImpl.java:44)
    at org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl.<init>(TaskAttemptContextImpl.java:39)

'super(conf，taskId.getJobID());'引发异常，很可能是因为taskId为null.

'super(conf, taskId.getJobID());' is throwing the exception, most likely because taskId is null.

推荐答案

我通过浏览HiveHbaseTableInputFormat找到了答案.由于我的解决方案针对蜂巢，因此效果很好.

I found the answer by looking through HiveHbaseTableInputFormat. Since my solution is targeted for hive, this works perfectly.

 TaskAttemptContext tac = ShimLoader.getHadoopShims().newTaskAttemptContext(
        job.getConfiguration(), reporter);

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