Comment by sethev

These analogies (except for DNS, perhaps) aren't very illuminating on the difference between a CP system and an AP system in the CAP sense, though. In banking, there are multiple parties involved. Each of those parties is likely running a CP system for their transactions (almost guaranteed). Same with stock exchanges - you can look up Martin Thompson's work for a public glimpse of how these systems work (LMAX and Aeron are systems related to this).

These examples are closer to control loops, where a decision is made and then carried out or finalized later. This kind of "eventual consistency" is pervasive but also significantly easier to reason about than what people usually mean by that term when talking about a distributed database, for example.

To expand on the 24/7 grocery store example: if the database with prices is consistent, you will always know what the current price is supposed to be. If the database is eventually consistent, you may get inconsistent answers about the current price that have to be resolved in the code somehow. That's way harder to reason about then "the price changed, but the tag hasn't been hung yet". The first case, professional software engineers struggle to deal with correctly. The second case, anyone can understand.