On Mixing Eventual and Strong Consistency: Acute Cloud Types

In this article we study the properties of distributed systems that mix eventual and strong consistency. We formalize such through acute cloud types (ACTs), abstractions similar to conflict-free replicated data types (CRDTs), which by default work in a highly available, eventually consistent fashion, but also feature strongly operations for tasks require global agreement. Unlike other mixed-consistency solutions, ACTs can rely on efficient quorum-based protocols, as Paxos. Hence, gracefully tolerate machine network failures operations. formally demonstrate phenomena are neither present purely nor systems. particular, identify xmlns:xlink="http://www.w3.org/1999/xlink">temporary operation reordering , implies interim disagreement between replicas relative order client requests were executed. When not handled carefully, phenomenon may lead undesired anomalies, including circular causality. prove an impossibility result states temporary reordering is unavoidable with sufficiently complex semantics. Our startling, because it shows apparent xmlns:xlink="http://www.w3.org/1999/xlink">strengthening semantics system (by introducing system) results weakening guarantees