37,690 research outputs found
The Weakest Failure Detector for Eventual Consistency
In its classical form, a consistent replicated service requires all replicas
to witness the same evolution of the service state. Assuming a message-passing
environment with a majority of correct processes, the necessary and sufficient
information about failures for implementing a general state machine replication
scheme ensuring consistency is captured by the {\Omega} failure detector. This
paper shows that in such a message-passing environment, {\Omega} is also the
weakest failure detector to implement an eventually consistent replicated
service, where replicas are expected to agree on the evolution of the service
state only after some (a priori unknown) time. In fact, we show that {\Omega}
is the weakest to implement eventual consistency in any message-passing
environment, i.e., under any assumption on when and where failures might occur.
Ensuring (strong) consistency in any environment requires, in addition to
{\Omega}, the quorum failure detector {\Sigma}. Our paper thus captures, for
the first time, an exact computational difference be- tween building a
replicated state machine that ensures consistency and one that only ensures
eventual consistency
Transaction Propagation on Permissionless Blockchains: Incentive and Routing Mechanisms
Existing permissionless blockchain solutions rely on peer-to-peer propagation
mechanisms, where nodes in a network transfer transaction they received to
their neighbors. Unfortunately, there is no explicit incentive for such
transaction propagation. Therefore, existing propagation mechanisms will not be
sustainable in a fully decentralized blockchain with rational nodes. In this
work, we formally define the problem of incentivizing nodes for transaction
propagation. We propose an incentive mechanism where each node involved in the
propagation of a transaction receives a share of the transaction fee. We also
show that our proposal is Sybil-proof. Furthermore, we combine the incentive
mechanism with smart routing to reduce the communication and storage costs at
the same time. The proposed routing mechanism reduces the redundant transaction
propagation from the size of the network to a factor of average shortest path
length. The routing mechanism is built upon a specific type of consensus
protocol where the round leader who creates the transaction block is known in
advance. Note that our routing mechanism is a generic one and can be adopted
independently from the incentive mechanism.Comment: 2018 Crypto Valley Conference on Blockchain Technolog
System Description for a Scalable, Fault-Tolerant, Distributed Garbage Collector
We describe an efficient and fault-tolerant algorithm for distributed cyclic
garbage collection. The algorithm imposes few requirements on the local
machines and allows for flexibility in the choice of local collector and
distributed acyclic garbage collector to use with it. We have emphasized
reducing the number and size of network messages without sacrificing the
promptness of collection throughout the algorithm. Our proposed collector is a
variant of back tracing to avoid extensive synchronization between machines. We
have added an explicit forward tracing stage to the standard back tracing stage
and designed a tuned heuristic to reduce the total amount of work done by the
collector. Of particular note is the development of fault-tolerant cooperation
between traces and a heuristic that aggressively reduces the set of suspect
objects.Comment: 47 pages, LaTe
A distributed optimization framework for localization and formation control: applications to vision-based measurements
Multiagent systems have been a major area of research for the last 15 years. This interest has been motivated by tasks that can be executed more rapidly in a collaborative manner or that are nearly impossible to carry out otherwise. To be effective, the agents need to have the notion of a common goal shared by the entire network (for instance, a desired formation) and individual control laws to realize the goal. The common goal is typically centralized, in the sense that it involves the state of all the agents at the same time. On the other hand, it is often desirable to have individual control laws that are distributed, in the sense that the desired action of an agent depends only on the measurements and states available at the node and at a small number of neighbors. This is an attractive quality because it implies an overall system that is modular and intrinsically more robust to communication delays and node failures
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