Semi-joins is the most used technique to optimize the treatment of complex relational queries on distributed architectures. However the overcost related to semi-joins computation can be very high due to data skew and to the high cost of communication in distributed architectures. In this paper we present a parallel equi-semi-join algorithm for shared nothing machines. The performance of this algorithm is analyzed using the BSP cost model and is proved to have asymptotic optimal complexity and perfect load balancing even for highly skewed data. This guarantees unlimited scalability in all situations for this key algorithm.
