Renaming is weaker than set agreement but for perfect renaming: a map of sub-consensus tasks

  • Authors:
  • Armando Castañeda;Damien Imbs;Sergio Rajsbaum;Michel Raynal

  • Affiliations:
  • IRISA-INRIA, Rennes Cedex, France;IRISA-INRIA, Rennes Cedex, France;Instituto de Matemáticas, UNAM, México City, México;Institut Universitaire de, France and IRISA-INRIA, Rennes Cedex, France

  • Venue:
  • LATIN'12 Proceedings of the 10th Latin American international conference on Theoretical Informatics
  • Year:
  • 2012

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Abstract

In the wait-free shared memory model substantial attention has been devoted to understanding the relative power of sub-consensus tasks. Two important sub-consensus families of tasks have been identified: k-set agreement and M-renaming. When 2≤k≤n−1 and n≤M≤2n−2, these tasks are more powerful than read/write registers, but not strong enough to solve consensus for two processes. This paper studies the power of renaming with respect to set agreement. It shows that, in a system of n processes, n-renaming is strictly stronger than (n−1)-set agreement, but not stronger than (n−2)-set agreement. Furthermore, (n+1)-renaming cannot solve even (n−1)-set agreement. As a consequence, there are cases where set agreement and renaming are incomparable when looking at their power to implement each other.