论文标题

使用转子步行的确定性自调整树网络

Deterministic Self-Adjusting Tree Networks Using Rotor Walks

论文作者

Avin, Chen, Bienkowski, Marcin, Salem, Iosif, Sama, Robert, Schmid, Stefan, Schmidt, Paweł

论文摘要

我们重新审视自调整的单源树网络的设计。该问题可以看作是对树的经典列表更新问题的概括,并在可重构数据中心网络中找到了应用程序。给我们一个固定的平衡二进制树T连接N节点V = {V_1,...,V_N}。源节点v_0,附加到树的根部,以在线和对抗性方式向V中的节点发出通信请求;请求对节点V的访问成本由T中V当前的深度给出。在线算法可以通过执行交换操作来降低访问成本,并通过其在树中与父母的位置交换。交换操作的费用为一个单位。目的是设计一种在线算法,该算法将总访问成本加上调整成本(交换)最小化。 Avin等。最近提出了随机步行的Random-Push,这是该问题的持续竞争性在线算法,以及利用随机步行的最新使用(MRU)属性的分析。 我们在分析和经验上研究此问题的在线算法。特别是,我们探讨了如何取代随机孔。我们考虑了一种简单的降低算法,我们称之为转子孔,因为它的行为让人联想到转子步行。我们首先证明转子孔具有持续的竞争:其竞争比率为12,因此比最佳现有竞争比低5倍。与Random-Push相反,该算法不具有MRU属性,这需要新的分析。我们对随机算法进行了显着改进,更简单的分析,表明它具有16竞争力。我们从经验上比较了所有自调整的单源树网络,使用具有不同位置的合成和真实数据,并观察到rotor-push和Randan-Push的性能几乎相同。

We revisit the design of self-adjusting single-source tree networks. The problem can be seen as a generalization of the classic list update problem to trees, and finds applications in reconfigurable datacenter networks. We are given a fixed balanced binary tree T connecting n nodes V = {v_1, ... , v_n}. A source node v_0, attached to the root of the tree, issues communication requests to nodes in V, in an online and adversarial manner; the access cost of a request to a node v, is given by the current depth of v in T. The online algorithm can try to reduce the access cost by performing swap operations, with which the position of a node is exchanged with the position of its parent in the tree; a swap operation costs one unit. The objective is to design an online algorithm which minimizes the total access cost plus adjustment cost (swapping). Avin et al. recently presented Random-Push, a constant competitive online algorithm for this problem, based on random walks, together with an analysis exploiting the most recently used (MRU) property of random walks. We study analytically and empirically, online algorithms for this problem. In particular, we explore how to derandomize Random-Push. We consider a simple derandomized algorithm which we call Rotor-Push, as its behavior is reminiscent of rotor walks. We first prove that Rotor-Push is constant competitive: its competitive ratio is 12 and hence by a factor of five lower than the best existing competitive ratio. In contrast to Random-Push, the algorithm does not feature the MRU property, which requires a new analysis. We present a significantly improved and simpler analysis for the randomized algorithm, showing that it is 16-competitive. We compare empirically all self-adjusting single-source tree networks, using synthetic and real data with varying locality and observe that Rotor-Push and Random-Push have almost identical performance.

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