Linearizability in distributed systems
On first reading (and probably on the second and third...) this sounds a bit abstract, but it really is all there is to it. A slightly different way to think about it is - a linearizable system appears as if there's only one copy of data in existence, and all client operations apply to this data atomically. This post dives deeper into what this means in practice.
Linearizability is a single-object consistency model (see the "Linearizability vs. Serializability" section below for more on this). It's common in distributed systems literature to talk about a register - a single key-value pair, for example, stored in some distributed database. When clients write and read this register concurrently, we can analyze the history of operations and their results and determine if the system maintains linearizability.
The following diagram describes a sequence of register reads and writes by three different clients; some of these operations are done concurrently. Time flows from left to right, and a colored rectangle denotes an operation; its left edge is the operation's start, and its right edge the operation's completion [2].
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