  We consider online preemptive scheduling of jobs arriving one by one, to be
assigned to two identical machines, with the goal of makespan minimization. We
study the effect of selecting the best solution out of two independent
solutions constructed in parallel in an online fashion. Two cases are analyzed,
where one case is purely online, and in the other one jobs are presented sorted
by non-increasing sizes. We show that using two solutions rather than one
improves the performance significantly, but that an optimal solution cannot be
obtained for any constant number of solutions constructed in parallel. Our
algorithms have the best possible competitive ratios out of algorithms for each
one of the classes.
