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The purpose of this paper is to discuss the limitations imposed by introducing fault-tolerance in a partial replication system which aims to provide causal consistency. The general outcome is that, to provide support for indefinite replica-failure, the notion of partial in partial replication becomes not-really-partial-at-all. We prove that to implement causal consistency when indefinite replica-failures are possible, it is impossible to respect the concept of genuine partial replication-not storing or propagating operations which are on objects a given replica does not replicate locally. In our initial approach to tackle this issue client replicas need only to replicate the operations they depend on which have not yet been marked as durable by the centralised component. We discuss remaining limitations and expected improvements in future work. CCS Concepts: • Computer systems organization → Peerto-peer architectures; Distributed architectures; Availability.

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In the last few years, causal consistency has become a popular consistency model for geo-replicated databases. The algorithms proposed to enforce causal consistency typically associate with each operation some metadata, which is used to guarantee that an operation is not executed if its execution would break causality. This may lead to the impression that causal consistency is intrinsically costly and non scalable. In this paper, we analyze the metadata costs of enforcing causal consistency and put these costs in perspective, considering the metadata that is necessary to enforce reliability. We show that by wisely ordering the propagation of operations it is possible to enforce causal consistency without any additional metadata other than the already necessary to enforce reliability. CCS Concepts: • Computer systems organization → Peerto-peer architectures; Distributed architectures; Reliability.