Consistency Failure

Category: When Analytics Does Not Work

Many analytics systems operate over distributed networks. As such, there may be cases where part of the network fails. This creates the possibility of a consistency failure, that is, when the state recorded by one part of the network is different from the state recorded by the other part of the network. The issue lies in how to resolve consistency failures. The CAP Theorem, also known as Brewer's conjecture, asserts that "it is impossible for a web service to provide the following three guarantees: consistency, availability, and partition-tolerance" (Gilbert & Lynch, 2002).

Consistency is handled in distributed systems with things like 'warranties' and 'promises'. A 'warranty' is an assertion by a subsystem that a certain value will not change before a specified time (Liu, et.al., 2014). A 'promise' is an assertion by a subsystem that the outcome of an operation is pending, but will become available at a future time (Mozilla, 2020). As the names of these terms imply, a distributed system must be capable of fulfilling warranties and promises; ethical questions arise when warranties and promises are, for whatever reason, unfulfilled.

Inconsistency can magnify ethical issues, especially in real-time analytics. "'When the facts change, I change my mind' can be a reasonable defence: but in order to avoid less defensible forms of inconsistency, changing your mind about one thing may require changing it about others also" (Boyd, 2019). Moral uncertainty, in other words, can have a cascading effect. Hence ethical analytics require mechanisms supporting warranties and promises.

Examples and Articles

Understanding Consistency
Nader Medhat, Mar 29 , 2021. Medium. "Consistency states that data cannot be written that would violate the rules for valid data." Direct Link

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