Vote Assignments Research Articles

Optimal binary vote assignment for replicated data

Data replication can be used to improve the availability of data in a distributed database system. In such a system, a mechanism is required to maintain the consistency of the replicated data. Weighted voting is a popular solution for maintaining the consistency. The performance of a voting system is determined by the vote assignment. It was shown in previous studies that finding the optimal solution among nonnegative integer vote assignments requires O(2 N 2 ) time. So it is not suitable to find the optimal integer vote assignment (OIVA) for large systems. In this paper, we propose the optimal binary vote assignment (OBVA) considering only binary vote assignments. It is shown that OBVA can achieve nearly the same availability of OIVA. On the other hand, OBVA requires only O( N 2) time, which is preferred for large systems.

New Heuristics for the Multidimensional Vote Assignment Problem

Vote assignments are being used for the design of fault tolerant systems. They work in such a way that every node in a computer network gets assigned a certain number of votes. Furthermore, a quorum is defined. A transaction can only take place if the number of votes collected is greater than or equal to the quorum. These single dimensional vote assignments provide a compact representation of certain antichains, namely those which consist of the minimal sets of nodes achieving the quorum. Multidimensional (MD) vote assignments are a generalization of single dimensional vote assignments. In contrast to single dimensional vote assignments, MD vote assignments have the important property that every antichain has a corresponding MD vote assignment and vice versa. For the efficient design of fault tolerant systems, it is important that the dimension of a MD vote assignment is as small as possible. We introduce some new heuristics for calculating a MD vote assignment which perform better than the heuristics known so far.

A short technical paper: Determining whether a vote assignment is dominated

One way to achieve mutual exclusion in a distributed system is to assign votes to each site in the system. If the total number of votes is odd, the assignment is known to be nondominated, meaning that no other assignment can provide strictly greater access and still achieve mutual exclusion. We characterize in this note dominated even-totaled vote assignments. As a consequence, we obtain that the problem of determining whether an even-totaled vote assignment is dominated is trivial if each site is assigned exactly one vote; however, the problem is NP-complete in general.

Vote assignments in weighted voting mechanisms

It is shown that voting can provide the maximum reliability if all nodes have reliability p>or=0.5. Thus, a system designer only needs to consider vote assignments in implementing mutual exclusion mechanisms. Some effective vote assignment algorithms are proposed. Neglecting link failures, it is found that the voting weight for each node can be determined by computing a logarithmic function of local information. Voting operations are formally defined, and an optimization objection function is formulated. A sufficient condition for optimal vote assignment and optimal sets of groups is presented, and it is shown that predefining a set of groups to achieve mutual exclusion is not feasible for a large system. Some algorithms generating optimal or suboptimal assignments for systems with perfect links are proposed. Some variations for systems with imperfect links are discussed, along with some comparisons of the new algorithms against previous algorithms proposed for the problem. >

Increasing availability under mutual exclusion constraints with dynamic vote reassignment

Voting is used commonly to enforce mutual exclusion in distributed systems. Each node is assigned a number of votes, and only the group with a majority of votes is allowed to perform a restricted operation. This paper describes techniques for dynamically reassigning votes upon node or link failure, in an attempt to make the system more resilient to future failures. We focus on autonomous methods for achieving this, that is, methods that allow the nodes to make independent choices about changing their votes and picking new vote values, rather than group consensus techniques that require tight coordination among the remaining nodes. Protocols are given which allow nodes to install new vote values while still maintaining mutual exclusion requirements. The lemmas and theorems to validate the protocols are presented. A simple example shows how to apply the method to a database object-locking scheme; the protocols, however, are versatile andgeneral purpose, and can be used foranyapplication requiring mutual exclusion. In addition, policies are presented that allow nodes to autonomously select their new vote values. Simulation results are presented comparing the autonomous methods to static vote assignments and to group consensus strategies. These results demonstrate that under high failure rates, dynamic vote reassignment shows great improvement over a static assignment of votes in terms of availability. In addition, many autonomous methods for determining a new vote assignment yield almost as much availability as a group consensus method and at the same time are faster and more flexible.

The Reliability of Voting Mechanisms

In a faulty distributed system, voting is commonly used to achieve mutual exclusion among groups of isolated nodes. Each node is assigned a number of votes, and any group with a majority of votes can perform the critical operations. Vote assignments can have a significant impact on system reliability. In this paper we address the problem of selecting vote assignments in order to maximize the probability that the critical operations can be performed at a given time by some group of nodes. We suggest simple heuristics to assign votes, and show that they give good results in most cases. We also study three particular homogeneous topologies (fully connected, Ethernet, and ring networks), and derive analytical expressions for system reliability. These expressions provide useful insights into the reliability provided by voting mechanisms.

The vulnerability of vote assignments

In a faulty distributed system, voting is commonly used to achieve mutual exclusion among groups of nodes. Each node is assigned a number of votes, and any group with a majority of votes can perform the critical operations. Vote assignments can have a significant impact on system reliability, and in this paper we study the vote assignment problem. To compare vote assignments we define two deterministic measures, node and edge vulnerability. We present various properties of these measures and discuss how they can be computed. For these measures we discuss the selection of the best assignment and propose heuristics to identify good candidate assignments.