Distributed Cache(Map side Joins) - mapreduce

Question

I would like to know more about DistributedCache concept in Mapreduce.
In my Mapper class below i wrote a logic to read a file that is available in cache.
protected void setup(Context context) throws IOException,
InterruptedException {
super.setup(context);
localFiles =DistributedCache.getLocalCacheFiles(context.getConfiguration());
for(Path myfile:localFiles)
{
String line=null;
String nameofFile=myfile.getName();
File file =new File(nameofFile);
FileReader fr= new FileReader(file);
BufferedReader br= new BufferedReader(fr);
line=br.readLine();
while(line!=null)
{
String[] arr=line.split("\t");
myMap.put(arr[0], arr[1]);
line=br.readLine();
}
}
}
Can someone tell me when will the above setUp(context) method gets called. Is that setUP(context) method called only once or for every map task that setup(context) method will run?

Answer 1

It's called per Mapper task or Reducer task only once. So if 10 mappers or reducers were spawned for a job, then for each mapper and reducer it will be called once.
General guidelines for what to add in this method, is any task that is required to do once can be written here, e.g. getting path of Distributed cache, Passing and getting parameters to mappers and reducers.
Similar is for cleanup method.