Towards a scalable, distributed metadata service for causal consistency under partial geo-replication

Bravo, Manual;Rodrigues, Luís;Van Roy, Peter
(2015) Middleware ’15: 16th International Middleware Conference — Location: Vancouver BC Canada

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  • Bravo, ManualUniversidade de Lisboa
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  • Rodrigues, LuísUniversidade de Lisboa
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Abstract
Causal consistency is a consistency criteria of practical relevance in geo-replicated settings because it provides well-defined semantics in a scalable manner. In fact, it has been proved that causal consistency is the strongest consistency model that can be enforced in an always-available system. Previous approaches to provide causal consistency, which successfully tackle the problem under full geo-replication, have unveiled the inherent tradeoff between the concurrency that the system allows and the size of the metadata needed to enforce causality. When the metadata is compressed, information about concurrency may be lost, creating false dependencies, i.e., the encoding may suggest a causal relation that does not exist in reality. False dependencies may cause artificial delays when processing requests, and decrease the quality of service experienced by the clients. Nevertheless, whether is possible to design a scalable solution that only uses an almost negligible amount of metadata and it is still capable of achieving high levels of concurrency under partial geo-replication, an increasingly relevant setting, remains as a challenging and interesting open research question. This position paper reports on the on-going development of Saturn, a metadata service for geo-replicated systems, that aims at mitigating the effects of false dependencies while keeping the metadata size small (even for challenging settings as partial geo-replication).
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Bravo, M., Rodrigues, L., & Van Roy, P. (2015). Towards a scalable, distributed metadata service for causal consistency under partial geo-replication. In Ivan Beschastnikh, Wouter Joosen (ed.), Proceedings of the Doctoral Symposium of the 16th International Middleware Conference. Association for Computing Machinery. https://doi.org/10.1145/2843966.2843971