Average_Sort

1. Goal : calculate the average of occurrences and sort them by multiple reducers
2. Contains 2 jobs
   • Job 1: Calculate Average
     • customized Partitioner, data type
   • Job 2: Sort the average outputs from Job1
     • customized Partitioner, data type, key class

To Calculate average value of each word

• The input contains many word-value pairs
• Speedup by Combiner
• Word only start by [a-z]

Job1

1. TextInputFormat
   • Converts every row of the source file
   • LongWritable key represents the offset of the record
   • Text value represents the entire record itself
2. Use KeyValueTextInputFormat
   • Extended version of TextInputFormat
   • Split the record with a fixed delimiter (Default: “\t”)
   • <Text, Text> pair
3. Components
   • Mapper
   • Partitioner
   • Combiner: merge result of same keys in map stage
   • Reducer: parse int from arg[3]
   • Customized Value Class
   • SumCountPair: <sum, count>
   • Data type
   • Average: Double

Job2

1. Sort
   • Input is the key-value output from Job1
   • Order by average values (from big to small)
   • With words in same average, order by lexicographically in ascending order (java string compare)
   • Support multiple reducers(2~5)
2. Sort by customized key class
   • Implement WritableComparable
   • Override compare function
   • Mapper output : <SortPair, NullWritable>
3. Total order sort
   • Assign ranges for each reducer in Paritioner
4. Components
   • Mapper
   • Partitioner
   • Reducer
5. Customized Key Class
   • SortPair <word, average>
   • implements WritableComparable
   • function comapreTo: return negative value for ascending order
6. Execution (in Average_Sort/)

   • make clean

     make

     sh execute.sh {iter_num, defualt=3}