Encontrados 15 documentos, a visualizar página 1 de 2
Improving the scalability of cloud-based resilient database servers
Soares, L.; Pereira, José, 1973-Many rely now on public cloud infrastructure-as-a-service for database servers, mainly, by pushing the limits of existing pooling and replication software to operate large shared-nothing virtual server clusters. Yet, it is unclear whether this is still the best architectural choice, namely, when cloud infrastructure provides seamless virtual shared storage and bills clients on actual disk usage. This paper addr...
An object mapping for the Cassandra distributed database
Gomes, Pedro; Pereira, José, 1973-; Oliveira, Rui Carlos Mendes deNew data management systems aimed at huge amounts of data, such as those pioneered by Google, Amazon, and Yahoo, have recently motivated a profound revolution in database management. These systems are characterized by simple data and query models and by their relaxed consistency, that contrasts with the ubiquitous and widely known relational and ACID model. These changes, in combination with the absence of a hi...
Worldwide consensus
Maia, Francisco; Matos, Miguel; Pereira, José, 1973-; Oliveira, Rui Carlos Mendes deConsensus is an abstraction of a variety of important challenges in dependable distributed systems. Thus a large body of theoretical knowledge is focused on modeling and solving consensus within different system assumptions. However, moving from theory to practice imposes compromises and design decisions that may impact the elegance, trade-offs and correctness of theoretical appealing consensus protocols. In t...
An epidemic approach to dependable key-value substrates
Matos, Miguel; Vilaça, Ricardo; Pereira, José, 1973-; Oliveira, Rui Carlos Mendes deThe sheer volumes of data handled by today's Internet services demand uncompromising scalability from the persistence substrates. Such demands have been successfully addressed by highly decentralized key-value stores invariably governed by a distributed hash table. The availability of these structured overlays rests on the assumption of a moderately stable environment. However, as scale grows with unprecedented...
A correlation-aware data placement strategy for key-value stores
Vilaça, Ricardo; Oliveira, Rui Carlos Mendes de; Pereira, José, 1973-Key-value stores hold the unprecedented bulk of the data produced by applications such as social networks. Their scalability and availability requirements often outweigh sacri cing richer data and pro- cessing models, and even elementary data consistency. Moreover, existing key-value stores have only random or order based placement strategies. In this paper we exploit arbitrary data relations easily expressed b...
Experimental evaluation of distributed middleware with a virtualized java envir...
Carvalho, Nuno; Bordalo, João; Campos, Filipe; Pereira, José, 1973-The correctness and performance of large scale service oriented systems depend on distributed middleware components performing various communication and coordination functions. It is, however, very difficult to experimentally assess such middleware components, as interesting behavior often arises exclusively in large scale settings, but such deployments are costly and time consuming. We address this challenge w...
A pragmatic protocol for database replication in interconnected clusters
Pereira, José, 1973-; Oliveira, Rui Carlos Mendes de; Grov, J.; Soares, L.; Correia Júnior, Alfrânio Tavares; Pedone, F.Multi-master update everywhere database replication, as achieved by protocols based on group communication such as DBSM and Postgres-R, addresses both performance and availability. By scaling it to wide area networks, one could save costly bandwidth and avoid large round-trips to a distant master server. Also, by ensuring that updates are safely stored at a remote site within transaction boundaries, disaster re...
Evaluating certification protocols in the partial database state machine
Sousa, António Luís Pinto Ferreira de; Moura, Francisco Coelho Soares; Pereira, José, 1973-; Oliveira, Rui Carlos Mendes dePartial replication is an alluring technique to ensure the reliability of very large and geographically distributed databases while, at the same time, offering good performance. By correctly exploiting access locality most transactions become confined to a small subset of the database replicas thus reducing processing, storage access and communication overhead associated with replication. The advantages of part...
Efficient epidemic multicast in heterogeneous networks
Pereira, José, 1973-; Oliveira, Rui Carlos Mendes de; Rodrigues, LuísThe scalability and resilience of epidemic multicast, also called probabilistic or gossip-based multicast, rests on its symmetry: Each participant node contributes the same share of bandwidth thus spreading the load and allowing for redundancy. On the other hand, the symmetry of gossiping means that it does not avoid nodes or links with less capacity. Unfortunately, one cannot naively avoid such symmetry withou...
Towards a generic group communication service
Pereira, José, 1973-; Carvalho, Nuno; Rodrigues, LuísView synchronous group communication is a mature technology that greatly eases the development of reliable distributed applications by enforcing precise message delivery semantics, especially in face of faults. It is therefore found at the core of multiple widely deployed and used middleware products. Although the implementation of a group communication system is a complex task, application developers may benef...
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