## The Queue-Read Queue-Write PRAM Model: Accounting for Contention in Parallel Algorithms (1997)

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Venue: | Proc. 5th ACM-SIAM Symp. on Discrete Algorithms |

Citations: | 23 - 10 self |

### BibTeX

@INPROCEEDINGS{Gibbons97thequeue-read,

author = {Phillip B. Gibbons and Yossi Matias and Vijaya Ramachandran},

title = {The Queue-Read Queue-Write PRAM Model: Accounting for Contention in Parallel Algorithms},

booktitle = {Proc. 5th ACM-SIAM Symp. on Discrete Algorithms},

year = {1997},

pages = {638--648}

}

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### Abstract

Abstract. This paper introduces the queue-read queue-write (qrqw) parallel random access machine (pram) model, which permits concurrent reading and writing to shared-memory locations, but at a cost proportional to the number of readers/writers to any one memory location in a given step. Prior to this work there were no formal complexity models that accounted for the contention to memory locations, despite its large impact on the performance of parallel programs. The qrqw pram model reflects the contention properties of most commercially available parallel machines more accurately than either the well-studied crcw pram or erew pram models: the crcw model does not adequately penalize algorithms with high contention to shared-memory locations, while the erew model is too strict in its insistence on zero contention at each step. The�qrqw pram is strictly more powerful than the erew pram. This paper shows a separation of log n between the two models, and presents faster and more efficient qrqw algorithms for several basic problems, such as linear compaction, leader election, and processor allocation. Furthermore, we present a work-preserving emulation of the qrqw pram with only logarithmic slowdown on Valiant’s bsp model, and hence on hypercube-type noncombining networks, even when latency, synchronization, and memory granularity overheads are taken into account. This matches the bestknown emulation result for the erew pram, and considerably improves upon the best-known efficient emulation for the crcw pram on such networks. Finally, the paper presents several lower bound results for this model, including lower bounds on the time required for broadcasting and for leader election.