Geographical Information Systems

Similarity Join for Big Geographic Data 35

After generating the groups in a reduce node, the MapReduce

framework calls the reduce function Reduce_base once for each group. This

function is presented in Algorithm 5. The function receives as input the

key-value pair (k2, v2List). k2 is the intermediate key of one of the records

of the group being processed and v2List is the list of values of all the

records of the group. If the size of the list is small enough to be processed

in a single node, the algorithm calls a single-node Similarity Join routine,

i.e., InMemorySimJoin, to get the links in the current partition (lines 1 to 2).

Otherwise all ...