alt Hacker NewsKind of annoying to read. No, the P in CAP theorem isn’t when the client can’t connect to your unavailable service. That would be the A. Maybe it was down because of a P on your side, but don’t start blaming your downtime on network partitions between the client and your service.
Edit: your service going down and not being able to take requests from clients does not a network partition make
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This is a common misunderstanding about the poorly named ‘Availability’ in CAP. Availability under CAP means that if your request reaches a non-failing node, that node still responds despite being unable to communicate with other nodes. This is distinct from SLA-style availability, which describes the uptime of the overall system. I’m pretty sure the partition tolerance they’re referring to is the fact that the tailnet remains intact and continues to operate even when nodes can’t reach the coordination service.
A network partition between the client and server is a network partition between two nodes in a distributed system, which is the P.
Isn't Availablility the ability to connect to something? If I'm calling from region A to region A servers, and the region A servers' networks go down. Well, my client is clever and can failover to region B servers. Except, all my state and context was on region A servers, and maybe that state wasn't replicated over to region B - that replication might only happen on a nightly basis.
When I reconnect, my dating profile is missing all the pictures I uploaded of me in my new convertible with me lowering my sunglasses and winking at the camera.
The LovinHuggin.com server architecture is Available, but not Partition Tolerant. And after I upload different pictures of me in tuxedos and talking like a boss on the cellphone to region B, I've potentially created a weird "split brain" situation. Region A and region B servers have different views of me. Both views are super hot, but the client might get confused if my session returns to region A when their network heals, and the nightly region replication might be messy with reconciling the split brain. Eventual consistency is a helpful (or fraught) feature to have in the database when things like split brain happen.