Maybe I'm missing something, but it seems like this is basically just glossing over this part:<p>> Some systems cannot be partitioned. Single-node systems (e.g., a monolithic Oracle server with no replication) are incapable of experiencing a network partition. But practically speaking these are rare;<p>I'm not sure how the writer came to the conclusion that these systems are rare. The website I'm working on now has a single monolithic Postgres server, and the majority of systems I've worked on connected to single monolithic datastores, so at the very least these systems exist. These aren't particularly <i>interesting</i> examples, but when talking theoretically like with the CAP theorem, you don't get to just ignore the rare or uninteresting cases. These seem like relatively common examples of choosing CA.<p>Of course, when you try to shard such databases, you're going to run into serious problems.<p>I guess the claim I can credit to the author is that CA <i>really really really</i> means <i>no partition tolerance</i>. <i>Even one network partition</i> puts you in CP or AP territory. But I don't think that means CA stores don't exist.<p>It may be that I'm just not understanding things correctly, though; the CAP paper is definitely a challenging read for me.
The implication derived from a trivial probability argument is misleading. Failures are correlated, so 1-(1-P)^n is an upper bound, firstly, but secondly and much more importantly, the value being computed is the wrong value. Failure of a node is not partition. To non-trivially partition a cluster of N nodes requires (N-2) failures, when the cluster is fully connected, for example (as e.g. on any bus network). Handling trival partition is, well, trivial, in some important senses.
It's worth keeping in mind that viewing a system as CP or AP usually isn't nuanced enough: <a href="https://martin.kleppmann.com/2015/05/11/please-stop-calling-databases-cp-or-ap.html" rel="nofollow">https://martin.kleppmann.com/2015/05/11/please-stop-calling-...</a>
Liked everything up to this part;<p>"When it comes to designing or evaluating distributed systems, then, I think we should focus less on which two of the three Virtues we like most and more on what compromises a system makes as things go bad."<p>It seemed like the entire point was that really there are only 2 Virtues (Consistency, Availability) and given a partition you will chose one or the other. The only database that doesn't have network partitions also isn't distributed.
The original CAP paper was intended as a high-level discussion item for students. Brewer has since emphasized that it is more of an academic approach than applicable to real-world distributed databases.<p>Other computer scientists have either modified or narrowed it to be more useful.<p>So it's fun to read the original CAP paper, but it's less useful than you would expect. When somebody asks me about CP vs. CA, I realize they in fact don't anything at all about distributed databases.