动态对等网络中的分布式协议
Distributed Agreement in Dynamic Peer-to-Peer Networks
摘要：
出于在高度动态的对等网络（P2P）中需要鲁棒和快速的分布式计算，我们研究了基本的分布式协议问题的算法。P2P网络是经历重节点{ \em churn}的高度动态的网络。我们的目标是设计快速的算法（运行在一个小的回合数），保证，尽管高节点流失率，几乎所有的节点达到一个稳定的协议。我们的主要贡献是随机分布式算法，保证{ \em稳定的几乎无处不在的协议}，即使在高对抗性的流失在一个多对数轮数：1。一种$O(\log^2 n)$循环（$n$是稳定的网络大小）随机算法，其在高达{ \em线性}扰动{ \em每循环}（即，$εn$，对于某个小常数$ε> 0$），假设流失是由不经意的对手控制的（该对手对什么节点加入和离开以及在什么时间加入和离开具有完全的知识和控制，并且具有无限的计算能力，但是对算法做出的随机选择不经意）。我们的算法只需要多对数的$n$位处理和发送（每轮）的每个节点。2.一种$O(\log m\log^3 n)$轮随机算法，在每轮高达$ε\sqrt{n}$扰动（对于一些小的$ε> 0$）的情况下以高概率实现几乎处处一致，其中$m$是输入值域的大小，即使在自适应对手（也知道算法所做的过去随机选择）下也能工作。该算法要求由每个节点处理和发送（每轮）高达$n$位（以及高达$O(\log m)$位）的多项式。
英文摘要：
Motivated by the need for robust and fast distributed computation in highly dynamic Peer-to-Peer (P2P) networks, we study algorithms for the fundamental distributed agreement problem. P2P networks are highly dynamic networks that experience heavy node {\em churn}. Our goal is to design fast algorithms (running in a small number of rounds) that guarantee, despite high node churn rate, that almost all nodes reach a stable agreement. Our main contributions are randomized distributed algorithms that guarantee {\em stable almost-everywhere agreement} with high probability even under high adversarial churn in a polylogarithmic number of rounds: 1. An $O(\log^2 n)$-round ($n$ is the stable network size) randomized algorithm that achieves almost-everywhere agreement with high probability under up to {\em linear} churn {\em per round} (i.e., $εn$, for some small constant $ε> 0$), assuming that the churn is controlled by an oblivious adversary (that has complete knowledge and control of what nodes join and leave and at what time and has unlimited computational power, but is oblivious to the random choices made by the algorithm). Our algorithm requires only polylogarithmic in $n$ bits to be processed and sent (per round) by each node. 2. An $O(\log m\log^3 n)$-round randomized algorithm that achieves almost-everywhere agreement with high probability under up to $ε\sqrt{n}$ churn per round (for some small $ε> 0$), where $m$ is the size of the input value domain, that works even under an adaptive adversary (that also knows the past random choices made by the algorithm). This algorithm requires up to polynomial in $n$ bits (and up to $O(\log m)$ bits) to be processed and sent (per round) by each node.
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