You want to populate an associative array in order to perform a map-side join. You've decided to put this information in a text file, place that file into the DistributedCache and read it in your…

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• Acombine
• Bmap
• Cinit
• Dconfigure

• A
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• B
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• C
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• D
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Explanation

Here is an illustrative example on how to use the DistributedCache: // Setting up the cache for the application 1. Copy the requisite files to the FileSystem: $ bin/hadoop fs -copyFromLocal lookup.dat /myapp/lookup.dat $ bin/hadoop fs -copyFromLocal map.zip /myapp/map.zip $ bin/hadoop fs -copyFromLocal mylib.jar /myapp/mylib.jar $ bin/hadoop fs -copyFromLocal mytar.tar /myapp/mytar.tar $ bin/hadoop fs -copyFromLocal mytgz.tgz /myapp/mytgz.tgz $ bin/hadoop fs -copyFromLocal mytargz.tar.gz /myapp/mytargz.tar.gz 2. Setup the application's JobConf: JobConf job = new JobConf(); DistributedCache.addCacheFile(new URI("/myapp/lookup.dat#lookup.dat"), job); DistributedCache.addCacheArchive(new URI("/myapp/map.zip", job); DistributedCache.addFileToClassPath(new Path("/myapp/mylib.jar"), job); DistributedCache.addCacheArchive(new URI("/myapp/mytar.tar", job); DistributedCache.addCacheArchive(new URI("/myapp/mytgz.tgz", job); DistributedCache.addCacheArchive(new URI("/myapp/mytargz.tar.gz", job); 3. Use the cached files in the Mapper or Reducer: public static class MapClass extends MapReduceBase implements Mapper<K, V, K, V> { private Path[] localArchives; private Path[] localFiles; public void configure(JobConf job) { // Get the cached archives/files localArchives = DistributedCache.getLocalCacheArchives(job); localFiles = DistributedCache.getLocalCacheFiles(job); public void map(K key, V value, OutputCollector<K, V> output, Reporter reporter) throws IOException { // Use data from the cached archives/files here output.collect(k, v);

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