Brandt's Tumblr

"A system that is not tolerant to network partitions can achieve data consistency and availability, and often does so by using transaction protocols. To make this work, client and storage systems must be part of the same environment; they fail as a whole under certain scenarios, and as such, clients cannot observe partitions. An important observation is that in larger distributed-scale systems, network partitions are a given; therefore, consistency and availability cannot be achieved at the same time. This means that there are two choices on what to drop: relaxing consistency will allow the system to remain highly available under the partitionable conditions, whereas making consistency a priority means that under certain conditions the system will not be available."

Eventually Consistent. Most of what I read about Amazon’s SimpleDB is immediately dismissive (and sometimes derisive) over the issue of “eventual consistency”. This quotation (which refers to the CAP theorem) concisely explains why it’s often appropriate to sacrifice immediate consistency for the sake of availability.