Tutorial: Consistency Choices in Modern Distributed Systems

Distributed systems underlying large-scale Internet services often guarantee immediate availability and tolerate network failures at the expense of providing only weak data consistency guarantees. This is compensated for by new programming constructs, such as replicated data types (aka CRDTs) and novel forms of transactions. Navigating the spectrum of possible consistency models and programming constructs is far from trivial. This tutorial surveys recent developments that help in this: formal definitions of consistency model semantics and methods for reasoning about how the weakness of consistency models affects the correctness of applications using them.