Document Type

Technical Report

Publication Date

1-1-1996

Technical Report Number

PCS-TR96-277

Abstract

Consensus, which requires processes with different input values to eventually agree on one of these values, is a fundamental problem in fault-tolerant computing. We study this problem in the context of asynchronous shared-memory systems. In our model, shared-memory consists of a sequence of cells and supports a specific set of operations. Prior research on consensus focussed on its solvability in shared-memories supporting specific operations. In this paper, we investigate the following general question: Let OP1 and OP2 be any two sets of operations such that each set includes read and write operations. Suppose there is no consensus protocol for N processes in a shared-memory that supports only operations in OP1 and in a shared-memory that supports only operations in OP2. Does it follow that there is no consensus protocol for N processes in a shared-memory that supports all operations in OP1 and all operations in OP_2? This question is in the same spirit as the robustness question, but there are significant differences, both conceptually and in the models of shared-memory for which the two questions are studied. For deterministic types, the robustness question has been known to have a positive answer, In contrast, we prove that the answer to the question posed above is negative even if operations are deterministic.

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