如何多次重复map/reduce任务

Question

为了多次重复相同的map/reduce任务，我应该把循环放在哪里?我知道它应该在主程序中，我不知道的是它应该在runJob周围还是其他地方?

Answer 1

这是一个很好的例子，从Thomas Jungblut的很棒的博客中摘录，我之前看到过:

while (counter > 0) {
   // reuse the conf reference with a fresh object
   conf = new Configuration();
   // set the depth into the configuration
   conf.set("recursion.depth", depth + "");
   job = new Job(conf);
   job.setJobName("Graph explorer " + depth);
   job.setMapperClass(ExplorationMapper.class);
   job.setReducerClass(ExplorationReducer.class);
   job.setJarByClass(ExplorationMapper.class);
   // always work on the path of the previous depth
   in = new Path("files/graph-exploration/depth_" + (depth - 1) + "/");
   out = new Path("files/graph-exploration/depth_" + depth);
   SequenceFileInputFormat.addInputPath(job, in);
   // delete the outputpath if already exists
   if (fs.exists(out))
    fs.delete(out, true);
   SequenceFileOutputFormat.setOutputPath(job, out);
   job.setInputFormatClass(SequenceFileInputFormat.class);
   job.setOutputFormatClass(SequenceFileOutputFormat.class);
   job.setOutputKeyClass(LongWritable.class);
   job.setOutputValueClass(VertexWritable.class);
   // wait for completion and update the counter
   job.waitForCompletion(true);
   depth++;
   counter = job.getCounters().findCounter(ExplorationReducer.UpdateCounter.UPDATED)
     .getValue();
}