Tight Analysis of Relaxed Multi-organization Scheduling Algorithms

The goal of this paper is to study how limited cooperation can impact the quality of the schedule obtained by multiple independent organizations in a typical grid computing platform. This relaxed version of the problem known as the Multi-Organization Scheduling Problem (MOSP) models an environment where organizations providing both resources and jobs tolerate a bounded degradation on the make span of their own jobs in order to minimize the make span over the entire platform. More precisely, the technical contributions are the following. First, we improve the existing in approximation bounds for this problem proving that what was previously though as not polynomially approximable ({\it unless $P=NP$}) is actually not approximable at all. We achieve this using two families of instances whose Pareto optimal solutions are on par with the previous in aproximability bounds. Then, we present two algorithms that solve the problem with approximation ratios of (2, 3/2) and (3, 4/3) respectively. This means that when using the first (second) algorithm, if an organization tolerates that the completion time of its last job cannot exceed twice (three times) the time it would have obtained by itself, then the algorithm provides a solution that is a 3/2-approximation (4/3-approximation) for the optimal global make span. Both algorithms are efficient since their performance ratio correspond to the Pareto optimal solutions of the previously defined instances.