Database replication protocols have historically been built on top of distributed database systems, and have consequently been designed and implemented using distributed transactional mechanisms, such as atomic commitment. We present the database state machine approach, a new way to deal with database replication in a cluster of servers. This approach relies on a powerful atomic broadcast primitive to propagate transactions between database servers, and no atomic commitment is necessary. Transaction commit is based on a certification test, and abort rate is reduced by the reordering certification test. The approach is evaluated using a detailed simulation model that shows the scalability of the system and the benefits of the reordering certification test.

This paper presents in detail an efficient and provably correct algorithm for database replication over partitionable networks. Our algorithm avoids the need for end-toend acknowledgments for each action while supporting network partitions and merges and allowing dynamic instantiation of new replicas. One round of end-to-end acknowledgments is required only upon a membership change event such as a network partition. New actions may be introduced to the system at any point, not only while in a primary component. We show how performance can be further improved for applications that allow relaxation of consistency requirements. We provide experimental results that demonstrate the efficiency of our approach.

Database replication protocols have historically been built on top of distributed database systems, and have consequently been designed and implemented using distributed transactional mechanisms, such as atomic commitment. We argue in this paper that this approach is not always adequate to efficiently support database replication and that more suitable alternatives, such as atomic broadcast primitives, should be employed instead. More precisely, we show in this paper that fully replicated database systems, based on the deferred update replication model, have better throughput and response time if implemented with an atomic broadcast termination protocol than if implemented with atomic commitment. 1 Introduction Replication is considered a cheap software based way to increase data availability when compared to hardware based specialised techniques [16]. However, designing a replication scheme that provides reasonable performance and maintains data consistency is still an active area of...

Epidemic-style (gossip-based) techniques have recently emerged as a scalable class of protocols for peer-to-peer reliable multicast dissemination in large process groups. These protocols provide probabilistic guarantees on reliability and scalability. However, existing implementations of epidemic-style dissemination are reputed to suffer from two major drawbacks: a) (Network Overhead) when deployed on a WAN-wide or VPN-wide scale they cause a large number of packets to transit across the boundaries of network domains (eg., LANs, subnets, ASs), causing an overload on core network elements such as bridges, routers, and links, and b) (Lack of Adaptivity) they impose the same load on process group members and the network regardless of the failure characteristics of the underlying network. In this paper, we report on the first comprehensive set of solutions to these problems. The solution includes two protocols: a) a Hierarchical Gossiping protocol, and b) an Adaptive multicast Dissemination Framework that can be used with any gossiping primitive. Our solution organizes nodes in a hierarchy which re ects the network topology and guarantees low trac across domain boundaries in the network. In the interests of space, this paper focuses on the Hierarchical Gossiping protocol in detail through mathematical and simulation analysis that evaluate the improvement over a traditional gossiping protocol. We present an overview of the working and properties of the Adaptive Dissemination protocol.

Distributed content-based publish-subscribe middleware provides the necessary decoupling, flexibility, expressiveness, and scalability required by modern distributed applications. Unfortunately, this kind of middleware usually does not provide reliability guarantees, as this problem has been thus far largely disregarded by the research community and solutions developed in other contexts are not immediately applicable.

The Unmanaged Internet Architecture (UIA) provides zero-configuration connectivity among mobile devices through personal names. Users assign personal names through an ad hoc device introduction process requiring no central allocation. Once assigned, names bind securely to the global identities of their target devices independent of network location. Each user manages one namespace, shared among all the user’s devices and always available on each device. Users can also name other users to share resources with trusted acquaintances. Devices with naming relationships automatically arrange connectivity when possible, both in ad hoc networks and using global infrastructure when available. A UIA prototype demonstrates these capabilities using optimistic replication for name resolution and group management and a routing algorithm exploiting the user’s social network for connectivity. 1

We introduce the hash history mechanism for capturing dependencies among distributed replicas. Hash histories, consisting of a directed graph of version hashes, are independent of the number of active nodes but dependent on the rate and number of modifications. We present the basic hash history scheme and discuss mechanisms for trimming the history over time. We simulate the efficacy of hash histories on several large CVS traces. Our results highlight a useful property of the hash history: the ability to recognize when two different non-commutative operations produce the same output, thereby reducing false conflicts and increasing the rate of convergence. We call these events coincidental equalities and demonstrate that their recognition can greatly reduce the time to global convergence.

Mainstream approaches to content-based distributed publish-subscribe typically route events deterministically based on information collected from subscribers, and do so by relying on a tree-shaped overlay network. While this solution achieves scalability in fixed, large-scale settings, it is less appealing in scenarios characterized by high dynamicity, e.g., mobile ad hoc networks or peer-to-peer systems. At the other extreme, researchers in the related fields of multicast and group communication have successfully exploited probabilistic techniques that provide increased fault tolerance, resilience to changes, and yet are scalable. In this paper, we propose a novel approach where event routing relies on deterministic decisions driven by a limited view on the subscription information and, when this is not sufficient, resorts to probabilistic decisions performed by selecting links at random. Simulations show that the particular mix of deterministic and probabilistic decisions we put forth in this work is very effective at providing high event delivery and low overhead in highly dynamic scenarios, without sacrificing scalability. 1.

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Gossip-based multicast can be an effective tool for providing highly reliable and scalable message dissemination. Previous work has shown it to be useful in a variety of group communication settings when processes all belong to a single process group. In this paper, we consider the problem of gossiping within overlapping process subgroups. If each subgroup independently runs the standard gossip protocol, then the total gossip overhead could be high for a process that is a member of many subgroups. We present anovel gossip protocol that allows individual subgroup members to trade-off update quality for gossip overhead, enabling processes to belong to several subgroups while maintaining a low total gossip overhead. Our results include a mathematical model for message dissemination under this modified gossip protocol, and an algorithm that computes gossip parameters such that all processes within a subgroup achieve their desired update quality. Preliminary results are promising.