Using parallel semi-join reduction to minimize distributed query response time

A one-shot semi-join reduction approach was recently proposed to execute all semi-joins on the same relation simultaneously such that the relation only needs to be scanned once. The one-shot semi-join reduction approach was applied to reducing distributed query response time under the assumption that one copy of each referenced relation has been chosen prior to the production of an execution plan. The estimations of both semi-join reduction effect and local join cost, employed in previous work, were restricted to a special case. In this paper, we extend the previous work in three ways: (1) remove the requirement for copy selection before the production of a semi-join reduction program, (2) allow the choice of redundant copies for the execution of semi-joins, (3) employ a general cost model which covers a large class of possible estimations of semi-join reduction effect and local join cost. Then, an algorithm to produce an optimal parallel one-shot semi-join reduction program for minimising response time shall be presented, addressing the above three aspects