A name-value pair associates a key with a corresponding value. In distributed word counting, each word becomes a key and the value 1 records one occurrence. section 13.9
Counting repeated words
A map task might produce [("the", 1), ("take", 1), ("the", 1)]. The reduce task groups the pairs by key and combines the values, producing [("the", 2)]. section 13.10
Name-value pairs support the two phases of the computation:
- Map tasks read text files, split them into words, and emit key-value pairs. section 13.10
- Reduce tasks collect values for each unique key and aggregate them into totals. section 13.10
