Reliable and total order broadcast in the crash-recovery model

This paper addresses the problems of broadcasting messages in a reliable and totally ordered manner assuming a crash-recovery model, i.e., a model where processes and channels may crash and possibly recover. We present a suite of specifications of reliable and total order broadcast abstractions for this model and we describe algorithms that implement those specifications. The properties of broadcast abstractions are first given separately and then composed: this provides a comprehensive design space for broadcast semantics. The algorithms we give are efficient both in terms of time-complexity (communication steps) and log-complexity (disk accesses).     

Processor membership in asynchronous distributed systems

Presents protocols for determining processor membership in asynchronous distributed systems that are subject to processor and communication faults. These protocols depend on the placement of a total order on broadcast messages. The types of systems for which each of these protocols is applicable are characterized by the properties of the communication mechanisms and by the availability of stable storage. In the absence of stable storage or of a mechanism for distinguishing promptly delivered messages, the authors show that no membership protocol can exist. They also discuss their experience in implementing these membership protocols     

Efficiently tolerating failures in asynchronous real-time distributed systems

We present a proactive resource allocation algorithm, called BEA, for fault-tolerant asynchronous real-time distributed systems. BEA considers an application model where trans-node application timeliness requirements are expressed using benefit functions, and anticipated workload during future time intervals are expressed using adaptation functions. Furthermore, BEA considers an adaptation model where subtasks of application tasks are replicated at run-time for tolerating failures as well as for sharing workload increases. Given such models, the objective of the algorithm is to maximize the aggregate real-time benefit and the ability to tolerate host failures during the time window of adaptation functions. Since determining the optimal solution is computationally intractable, BEA heuristically computes suboptimal resource allocations in polynomial-time. We show that BEA can achieve almost the same fault-tolerance ability as full replication, and accrue most of real-time benefit that full replication can accrue. In the meanwhile, BEA requires much fewer replicas than full replication, and hence is cost effective.     

Relationships between broadcast and shared memory in reliable anonymous distributed systems

We study the power of reliable anonymous distributed systems, where processes do not fail, do not have identifiers, and run identical programmes. We are interested specifically in the relative powers of systems with different communication mechanisms: anonymous broadcast, read-write registers, or read-write registers plus additional shared-memory objects. We show that a system with anonymous broadcast can simulate a system of shared-memory objects if and only if the objects satisfy a property we call idemdicence this result holds regardless of whether either system is synchronous or asynchronous. Conversely, the key to simulating anonymous broadcast in anonymous shared memory is the ability to count: broadcast can be simulated by an asynchronous shared-memory system that uses only counters, but read-write registers by themselves are not enough. We further examine the relative power of different types and sizes of bounded counters and conclude with a non-robustness result. James Aspnes is a Professor of Computer Science at Yale University. He received his Ph.D. from Carnegie-Mellon University in 1992. Faith Ellen Fich is a Professor of Computer Science at the University of Toronto. She received her Ph.D. from the University of California, Berkeley in 1982. Eric Ruppert was educated at the University of Toronto, where he completed his doctorate in 1999. He spent a year as a postdoctoral fellow at Brown University and is an Associate Professor at York University.     

Centralized asynchronous broadcast in radio networks

We study asynchronous broadcasting in packet radio networks. A radio network is represented by a directed graph, in which one distinguished source node stores a message that needs to be disseminated among all the remaining nodes. An asynchronous execution of a protocol is a sequence of events, each consisting of simultaneous deliveries of messages. The correctness of protocols is considered for specific adversarial models defined by restrictions on events the adversary may schedule. A protocol specifies how many times the source message is to be retransmitted by each node. The total number of transmissions over all the nodes is called the work of the broadcast protocol; it is used as complexity measure. We study computational problems, to be solved by deterministic centralized algorithms, either to find a broadcast protocol or to verify the correctness of a protocol, for a given network. The amount of work necessary to make a protocol correct may have to be exponential in the size of network. There is a polynomial-time algorithm to find a broadcast protocol for a given network. We show that certain problems about broadcasting protocols for given networks are complete in NP and co-NP complexity classes.     

Analysis of replication in distributed database systems

The authors develop an approximate analytical model to study the tradeoffs of replicating data in a distributed database environment. Several concurrency control protocols are considered, including pessimistic, optimistic, and semi-optimistic protocols. The approximate analysis captures the effect of the protocol on hardware resource contention and data contention. The accuracy of the approximation is validated through detailed simulations. It is found that the benefit of replicating data and the optimal number of replicates are sensitive to the concurrency control protocol. Under the optimistic and semi-optimistic protocols, replications can significantly improve response time with an additional MIPS (million instructions per second) requirement to maintain consistency among the replicates. The optimal degree of replication is further affected by the transaction mix (e.g. the fraction of read-only transactions), the communications delay and overhead, the number of distributed sites, and the available MIPS. Sensitivity analyses have been carried out to examine how the optimal degree of replication changes with respect to these factors     

Coding-based replication schemes for distributed systems

Data is often replicated in distributed systems to improve availability and performance. This replication is expensive in terms of disk storage since the existing schemes generally require full files to be stored at each site. In this paper, we present schemes which significantly reduce the storage requirements in replication based systems. These schemes use the coding method suggested by Rabin to store replicated data. The first scheme that we present is a modification of the simple voting algorithm and its quorum requirements. We then show how some of the extensions of the voting algorithm can also be modified to get storage efficient schemes for managing such replication. We evaluate the availability offered by these schemes and show that the storage space required to achieve certain availability are significantly lower than the conventional schemes with full file replication. Since coding is used, these schemes also provide a high degree of data security     

Non-blocking atomic commit in asynchronous distributed systems with failure detectors

This paper addresses the Non-Blocking Atomic Commit (NB-AC) problem in asynchronous distributed systems augmented with failure detectors. We first show that, in these systems, NB-AC and Consensus are incomparable. Roughly speaking, there is a failure detector that solves NB-AC but not Consensus and a failure detector that solves Consensus but not NB-AC. Then we introduce the Anonymously Perfect failure detector . We show that, to solve NB-AC, is necessary (while is not), whereas is sufficient when a majority of the processes are correct. We draw from our results some observations on the practical solvability of NB-AC. Received: August 2000 / Accepted: May 2001     

A Transactional Asynchronous Replication Scheme for Mobile Database Systems

In mobile database systems,mobility of users has a significant impact on data replication.As a result,the various replica control protocols that exist today in traditional distributed and multidatabase environments are no longer suitable To solve this problem,a new mobile database replication scheme,the Transaction-Level Result-Set Propagation(TLRSP)model,is put forward in this paper,The conflict dectction and resolution strategy based on TLRSP is discussed in detail,and the implementation algorithm is proposed,In order to compare the performance of the TLRSP model with that of other mobile replication schemes,we have developed a detailde simulation model.Experimantal results show that the TLRSP model provides an effcient support for replicated mobile database systems by reducing reprocessing overhead and maintaining database consistency.     

Managing transactions on grid-neighbour replication in distributed systems

Managing transactions is very important in distributed databases in order to preserve data consistency and reliability of the systems. This paper presents a new design to manage transactions on neighbour replication in a distributed database system. We address how to build a reliable system for managing transactions on a neighbour replication grid (NRG) in terms to preserve the data consistency and support fault-tolerance. We first recall the model and technique of NRG that impose neighbours binary vote assignment to its logical grid structure on data copies. We extend our work in managing transactions to normal and failure cases. Finally, the implementation of the system is presented.     

Quorum-based mutual exclusion in asynchronous distributed systems with unreliable failure detectors

This paper considers the fault-tolerant quorum-based mutual exclusion problem in a message-passing asynchronous system and determines a failure detector to solve the problem. This failure detector, which we call the modal failure detector star, and which we denote by M ^?, is strictly weaker than the perfect failure detector P but strictly stronger than the eventually perfect failure detector ?P. The paper shows that at any environment, the problem is solvable with M ^?. In addition, we make an analysis of our algorithm performance in terms of the number of messages and synchronization delay.     

The election problem in asynchronous distributed systems with bounded faulty processes

Determining the “weakest” failure detectors is a central topic in solving many agreement problems such as Consensus, Non-Blocking Atomic Commit and Election in asynchronous distributed systems. So far, this has been studied extensively for several such fundamental problems. It is stated that Perfect Failure Detector P is the weakest failure detector to solve the Election problem with any number of faulty processes. In this paper, we introduce Modal failure detector M and show that to solve Election, M is the weakest failure detector to solve election when the number of faulty processes is less than ⌈n/2⌉. We also show that it is strictly weaker than P.

Computing global functions in asynchronous distributed systems with perfect failure detectors

A Global Data is a vector with one entry per process. Each entry must be filled with an appropriate value provided by the corresponding process. Several distributed computing problems amount to compute a function on a global data. This paper proposes a protocol to solve such problems in the context of asynchronous distributed systems where processes may fail by crashing. The main problem that has to be solved lies in computing the global data and in providing each noncrashed process with a copy of it, despite the possible crash of some processes. To be consistent, the global data must contain, at least, all the values provided by the processes that do not crash. This defines the Global Data Computation (GDC) problem. To solve this problem, processes execute a sequence of asynchronous rounds during which they construct, in a decentralized way, the value of the global data and eventually each process gets a copy of it. To cope with process crashes, the protocol uses a perfect failure detector. The proposed protocol has been designed to be time efficient: it allows early decision. Let t be the maximum number of processes that may crash, t相似文献   

Efficient and stable quorum-based log replication and replay for modern cluster-databases

The modern in-memory database (IMDB) can support highly concurrent on-line transaction processing (OLTP) workloads and generate massive transactional logs per second. Quorum-based replication protocols such as Paxos or Raft have been widely used in the distributed databases to offer higher availability and fault-tolerance. However, it is non-trivial to replicate IMDB because high transaction rate has brought new challenges. First, the leader node in quorum replication should have adaptivity by considering various transaction arrival rates and the processing capability of follower nodes. Second, followers are required to replay logs to catch up the state of the leader in the highly concurrent setting to reduce visibility gap. Third, modern databases are often built with a cluster of commodity machines connected by low configuration networks, in which the network anomalies often happen. In this case, the performance would be significantly affected because the follower node falls into the long-duration exception handling process (e.g., fetch lost logs from the leader). To this end, we build QuorumX, an efficient and stable quorum-based replication framework for IMDB under heavy OLTP workloads. QuorumX combines critical path based batching and pipeline batching to provide an adaptive log propagation scheme to obtain a stable and high performance at various settings. Further, we propose a safe and coordination-free log replay scheme to minimize the visibility gap between the leader and follower IMDBs. We further carefully design the process for the follower node in order to alleviate the influence of the unreliable network on the replication performance. Our evaluation results with the YCSB, TPC-C and a realistic micro-benchmark demonstrate that QuorumX achieves the performance close to asynchronous primary-backup replication and could always provide a stable service with data consistency and a low-level visibility gap.     

Research and performance evaluation of data replication technology in distributed storage systems

Replication is a key technology of distributed storage systems. In this paper, an indirect replication algorithm is proposed following the intrinsic characteristic of distributed storage systems and the peer-to-peer model. In the indirect replication algorithm, the data object is partitioned into several data blocks. These data blocks are encoded in order that there is data redundancy between data blocks. Comparing with the traditional replication algorithm, the indirect replication algorithm has less granularity of replication, less bandwidth and storage costs, and provides higher availability, durability, and security. The performance evaluation shows that the encoding and decoding times are proportional to the data size, and that the irregular cascade bipartite graphs are of great advantage in improving the success ratio of data recovery. Finally, if the number of data blocks used to recover the data object is larger than a certain value, the success ratio of data recovery approaches 100%.     

基于星球机器人分布计算系统的原子组播协议

针对星球机器人分布计算系统容错的可靠组播通信,提出了一种基于向量时间的原子组组播协议.协议从星球机器人分布计算系统及通信模型的特点出发,使用向量时间和令牌进程来标识和保证全局投递顺序,通过令牌进程对不稳定消息的转发和两阶段提交来保证投递原子性和虚同步.模拟实验表明,协议提供了一个代价较小的可靠组播方法,具有快速和轻量的优点.     

Proactive resource allocation for asynchronous real-time distributed systems in the presence of processor failures

We present two proactive resource allocation algorithms, RBA^*-FT and OBA-FT, for fault-tolerant asynchronous real-time distributed systems. The algorithms consider an application model where task timeliness is specified by Jensen's benefit functions and the anticipated application workload during future time intervals is described by adaptation functions. In addition, we assume that reliability functions of processors are available a priori. Given these models, our objective is to maximize aggregate task benefit and minimize aggregate missed deadline ratio in the presence of processor failures. Since determining the optimal solution is computationally intractable, the algorithms heuristically compute sub-optimal resource allocations, but in polynomial time. Experimental results reveal that RBA^*-FT and OBA-FT outperform their non-fault-tolerant counterparts in the presence of processor failures. Furthermore, RBA^*-FT performs better than OBA-FT, although OBA-FT incurs better worst-case and amortized computational costs. Finally, we observe that both algorithms robustly withstand errors in the estimation of anticipated failures.     

Modelling and distributed simulation of asynchronous hardware

Synchronous VLSI design is approaching a critical point, with clock distribution becoming an increasingly costly and complicated issue and power consumption rapidly emerging as a major concern. Hence, recently, there has been a resurgence of interest in asynchronous digital design techniques as they promise to liberate VLSI systems from clock skew problems, offer the potential for low power and high performance and encourage a modular design philosophy which makes incremental technological migration a much easier task. This activity has revealed a need for modelling and simulation techniques suitable for the asynchronous design style. Contributing to the quest for modelling and simulation techniques suitable for asynchronous design, and motivated by the increasing debate regarding the potential of CSP for this purpose, this paper investigates the suitability of occam, a CSP-based programming language, for the modelling and simulation of complex asynchronous systems. A generic modelling framework is introduced and issues arising from the parallel semantics of CSP/occam when the latter is employed to perform simulation are addressed.     

Optimal NODUP all-to-all broadcast schemes in distributed computingsystems

Broadcast, referring to a process of information dissemination in a distributed system whereby a message originating from a certain node is sent to all other nodes in the system, is a very important issue in distributed computing. All-to-all broadcast means the process by which every node broadcasts its certain piece of information to all other nodes. In this paper, we first develop the optimal all-to-all broadcast scheme for the case of one-port communication, which means that each node can only send out one message in one communication step, and then, extend our results to the case of multi-port communication, i.e., k-port communication, meaning that each node can send out k messages in one communication step. We prove that the proposed schemes are optimal for the model considered in the sense that they not only require the minimal number of communication steps, but also incur the minimal number of messages