Application of Filters to Multiway Joins in MapReduce

Algorithm 4

Map function.

 ⊳𝑣𝑎𝑙𝑢𝑒: an input record from the 𝑖th dataset

 ⊳𝑟𝑒𝑝𝑙: replication factors that are pre-computed or pre-defined in the 𝑖𝑛𝑖𝑡 phase

(1) procedure  MAP(𝑘𝑒𝑦,𝑣𝑎𝑙𝑢𝑒)

(2)  extract the join attribute values 𝑗𝑜𝑖𝑛𝐴𝑡𝑡𝑟[1,…,𝑛] by parsing the input record 𝑣𝑎𝑙𝑢𝑒

             ⊳‖: concatenation, #: delimiter

(3)  𝑗𝑜𝑖𝑛𝐴𝑡𝑡𝑟𝐾𝑒𝑦← 𝑗𝑜𝑖𝑛𝐴𝑡𝑡𝑟[1] ‖#‖ ⋯ ‖#‖ 𝑗𝑜𝑖𝑛𝐴𝑡𝑡𝑟[𝑛]

(4)  𝑟𝑒𝑑𝑢𝑐𝑒𝑟𝐿𝑖𝑠𝑡←𝐹𝑖𝑛𝑑𝑇𝑎𝑟𝑔𝑒𝑡𝑅𝑒𝑑𝑢𝑐𝑒𝑟𝑠(𝑗𝑜𝑖𝑛𝐴𝑡𝑡𝑟,𝑟𝑒𝑝𝑙)

(5)  for each 𝑟𝑒𝑑𝑢𝑐𝑒𝑟 in 𝑟𝑒𝑑𝑢𝑐𝑒𝑟𝐿𝑖𝑠𝑡  do

            ⊳𝑡𝑎𝑔: the dataset id of the record

(6)   𝐸𝑚𝑖𝑡((𝑗𝑜𝑖𝑛𝐴𝑡𝑡𝑟𝐾𝑒𝑦,𝑟𝑒𝑑𝑢𝑐𝑒𝑟),(𝑣𝑎𝑙𝑢𝑒,𝑡𝑎𝑔))

(7)  end for

(8) end procedure