Parallel Online Algorithms for the Bin Packing Problem

We study parallel online algorithms: For some fixed integer k , a collective of k parallel processes that perform online decisions on the same sequence of events forms a k - copy algorithm . For any given time and input sequence, the overall performance is determined by the best of the k individual total results. Problems of this type have been considered for online makespan minimization; they are also related to optimization with advice on future events, i.e., a number of bits available in advance. Parallel online algorithms are also of interest in practical scenarios in which redundancy is used for hedging against undesired outcomes. We develop Predictive Harmonic _3 (PH3), a relatively simple family of k -copy algorithms for the online Bin Packing Problem, whose joint competitive factor converges to 1.5 for increasing k . In particular, we show that k=6 suffices to guarantee a factor of 1.5714 for PH3, which is better than 1.57829, the performance of the best known 1-copy algorithm Advanced Harmonic , while k=11 suffices to achieve a factor of 1.5406, beating the known lower bound of 1.54278 for a single online algorithm. In the context of online optimization with advice, our approach implies that 4 bits suffice to achieve a factor better than this bound of 1.54278, which is considerably less than the previous bound of 15 bits.