•In partitioning phase,
read+write both relations; 2(M+N). In matching phase, read both relations; M+N I/Os.
•In our running
example, this is a total of 4500 I/Os. (45 seconds!)
•Sort-Merge Join vs. Hash
Join:
–Given
a minimum amount of memory both have a cost of 3(M+N) I/Os.
Hash Join superior on this count if relation sizes differ
greatly. Also, Hash Join shown to be
highly parallelizable.
–Sort-Merge
less sensitive to data skew; result is sorted.