UNIVERSIDADE DE LISBOA INSTITUTO SUPERIOR TÉCNICO Fault-Tolerant Renaming in Synchronous Message-Passing Systems
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چکیده
Exploring the power and limitations of different coordination problems has always been at the heart of the theory of distributed computing. This thesis addresses the coordination problem called renaming, in which processes start with ids from a large namespace and output new names from a small namespace. Renaming can be seen as a dual to the classical consensus problem: instead of agreeing on a unique value, in renaming correct processes must disagree in a constructive way, by picking distinct values (names) from an appropriate range of values. We focus on synchronous message-passing systems, where n processes are arranged in a fully connected network and communicate by sending messages. We show that, with resort to randomization, renaming can be solved in O(log log n) rounds with high probability, if up to t < n may fail by crashing (t is an upper bound on the number of faults). In contrast, deterministic algorithms require Ω(log n) rounds [CHT99]. Thus, our result implies that randomized renaming algorithms can outperform deterministic algorithms by an exponential factor. When considering Byzantine faults, we show that randomized algorithms can solve renaming in O(log n) rounds with high probability, while tolerating up to t < n Byzantine faults (in contrast, deterministic algorithms require unbounded time [OBG08]). These results imply that randomization is a powerful and necessary technique in solving renaming. Finally, this thesis is the first to address order-preserving renaming in the context of Byzantine faults. In order-preserving renaming, processes must output new names in the order of their original ids. We show that renaming can be solved in O(log n) rounds, if up to t < n/3 processes may be Byzantine. We also show that order-preserving renaming
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تاریخ انتشار 2014