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They answer your question just two lines under the one you are quoting: > For distributed systems over a “wide area,” it's generally viewed that partitions are
by halflings 10y ago
They answer your question just two lines under the one you are quoting:
> For distributed systems over a “wide area,” it's generally viewed that partitions are inevitable, although not necessarily common. If you believe that partitions are inevitable, any distributed system must be prepared to forfeit either consistency (AP) or availability (CP), which is not a choice anyone wants to make. In fact, the original point of the CAP theorem was to get designers to take this tradeoff seriously. But there are two important caveats: First, you only need to forfeit consistency or availability during an actual partition, and even then there are many mitigations. Second, the actual theorem is about 100% availability; a more interesting discussion is about the tradeoffs involved to achieve realistic high availability.
- rdtsc 10y ago> If you believe that partitions are inevitable, any distributed system How does that answer it? Are they implying that partitions will not happen if you don't believe in them?
- robryk 10y agoA CA system is not a system that doesn't have partitions, it's a system that works under the condition that there are no partitions (ie. it is a non-partition-resistant system).
- sudhirj 10y agoA memcache cluster might qualify. If there's a partition, just forget about the missing nodes. It's just a cache anyway.
- krenoten 10y agoThe system you describe would typically be referred to as AP, because it maintains availability in the presence of partitions.
- rdtsc 10y ago> , it's a system that works under the condition that there are no partitions But that is not a choice with distributed systems, unless as soon as a partition happens the system shuts down immediately. That is it effectively disappears and never re-appears again. But that's not a CA system then? Or saying that it is not partition resistant is also difficult because the system in case of a partition will do _something_. The typical choices is that it either responds to clients (trying to be AP) or it doesn't (trying to be CP). That is why I understand CA systems as equivalent to the belief that "partitions can't happen". Which I think is unrealistic.
- robryk 10y agoThis is a system which is guaranteed to be consistent and available as long as there are no partitions. If there are partitions, the system isn't guaranteed to be either. Yes, it's a pretty much useless system.