Hadoop DistributedCache is deprecated - what is the preferred API?

My map tasks need some configuration data, which I would like to distribute via the Distributed Cache.

The Hadoop MapReduce Tutorial shows the usage of the DistributedCache class, roughly as follows:

// In the driver
JobConf conf = new JobConf(getConf(), WordCount.class);
...
DistributedCache.addCacheFile(new Path(filename).toUri(), conf); 

// In the mapper
Path[] myCacheFiles = DistributedCache.getLocalCacheFiles(job);
...

However, DistributedCache is marked as deprecated in Hadoop 2.2.0.

What is the new preferred way to achieve this? Is there an up-to-date example or tutorial covering this API?

Solution 1:

The APIs for the Distributed Cache can be found in the Job class itself. Check the documentation here: http://hadoop.apache.org/docs/stable2/api/org/apache/hadoop/mapreduce/Job.html The code should be something like

Job job = new Job();
...
job.addCacheFile(new Path(filename).toUri());

In your mapper code:

Path[] localPaths = context.getLocalCacheFiles();
...

Solution 2:

To expand on @jtravaglini, the preferred way of using DistributedCache for YARN/MapReduce 2 is as follows:

In your driver, use the Job.addCacheFile()

public int run(String[] args) throws Exception {
    Configuration conf = getConf();

    Job job = Job.getInstance(conf, "MyJob");

    job.setMapperClass(MyMapper.class);

    // ...

    // Mind the # sign after the absolute file location.
    // You will be using the name after the # sign as your
    // file name in your Mapper/Reducer
    job.addCacheFile(new URI("/user/yourname/cache/some_file.json#some"));
    job.addCacheFile(new URI("/user/yourname/cache/other_file.json#other"));

    return job.waitForCompletion(true) ? 0 : 1;
}

And in your Mapper/Reducer, override the setup(Context context) method:

@Override
protected void setup(
        Mapper<LongWritable, Text, Text, Text>.Context context)
        throws IOException, InterruptedException {
    if (context.getCacheFiles() != null
            && context.getCacheFiles().length > 0) {

        File some_file = new File("./some");
        File other_file = new File("./other");

        // Do things to these two files, like read them
        // or parse as JSON or whatever.
    }
    super.setup(context);
}

Solution 3:

The new DistributedCache API for YARN/MR2 is found in the org.apache.hadoop.mapreduce.Job class.

   Job.addCacheFile()

Unfortunately, there aren't as of yet many comprehensive tutorial-style examples of this.

http://hadoop.apache.org/docs/stable/api/org/apache/hadoop/mapreduce/Job.html#addCacheFile%28java.net.URI%29