Putting Consistency back into Eventual Consistency

Valter Balegas (1, 2) , Sérgio Duarte (2, 1) , Carla Ferreira (2, 1) , Rodrigo Rodrigues (2, 1) , Nuno Preguiça (2, 1) , Mahsa Najafzadeh (3) , Marc Shapiro (3)

1 CITI - CITI Centre of Innovation in Telecommunications and Integration of services
2 NOVA-LINCS - NOVA Laboratory for Computer Science and Informatics
3 Regal - Large-Scale Distributed Systems and Applications

Geo-replicated storage systems are at the core of current Internet services. The designers of the replication protocols used by these systems must choose between either supporting low-latency, eventually-consistent operations, or ensuring strong consistency to ease application correctness. We propose an alternative consistency model, Explicit Consistency, that strengthens eventual consistency with a guarantee to preserve specific invariants defined by the applications. Given these application-specific invariants, a system that supports Explicit Consistency identifies which operations would be unsafe under concurrent execution, and allows programmers to select either violation-avoidance or invariant-repair techniques. We show how to achieve the former, while allowing operations to complete locally in the common case, by relying on a reservation system that moves coordination off the critical path of operation execution. The latter, in turn, allows operations to execute without restriction, and restore invariants by applying a repair operation to the database state. We present the design and evaluation of Indigo, a middleware that provides Explicit Consistency on top of a causally-consistent data store. Indigo guarantees strong application invariants while providing similar latency to an eventually-consistent system in the common case.

Domaines: Informatique [cs]

Valter Balegas, Sérgio Duarte, Carla Ferreira, Rodrigo Rodrigues, Nuno Preguiça, et al.. Putting Consistency back into Eventual Consistency. European Conference on Computer Systems (EuroSys), ACM Sigops / EuroSys, Apr 2015, Bordeaux, France. pp.6:1--6:16, ⟨10.1145/2741948.2741972⟩. ⟨hal-01248191⟩