BTW, the original GFS relies on Chubby, which uses Paxos internally. I was kind of tempted to put "intelligibility" under physical limitations. Let's look at these in more detail. Since Dynamo is a complete system design, there are many different parts to look at beyond the core replication task. Or you might have some kind of communication system that makes it possible to assign sequential numbers as in a total order. Within each epoch, each proposal is numbered with a unique strictly increasing number. To the extent that we fail to understand and model time, our systems will fail. Let's contrast this with the second pattern - asynchronous replication (a.k.a. Perhaps the most obvious characteristic of systems that do not enforce single-copy consistency is that they allow replicas to diverge from each other. Ideally, we'd prefer the failure detector to be able to adjust to changing network conditions and to avoid hardcoding timeout values into it. This text is focused on distributed programming and systems concepts you'll need to understand commercial systems in the data center. E.g. In other use cases, the end user cannot really distinguish between a relatively recent answer that can be obtained cheaply and one that is guaranteed to be correct and is expensive to calculate. Dynamo prioritizes availability over consistency; it does not guarantee single-copy consistency. During normal operation, a partition-tolerant consensus algorithm is rather simple. This preview shows page 1 - 3 out of 78 pages. It starts with a Nietzsche quote, and then introduces system models and the many assumptions that are made in a typical system model. From a performance perspective, this means that the system is fast: the client does not need to spend any additional time waiting for the internals of the system to do their work. The two main alternatives are: The synchronous system model imposes many constraints on time and order. It has been implemented in Cassandra, where timing information is piggybacked on other messages and an estimate is calculated based on a sample of this information in a Monte Carlo simulation. And if you spot an error, file a pull request on Github. When a system does not track metadata, and only returns the value (e.g. We need one more thing to be able to make definite assertions: logical circumscription. This type of system can detect conflicting writes at some later point, but does not guarantee that the results are equivalent to some correct sequential execution. Work fast with our official CLI. ZAB. No leaf ever wholly equals another, and the concept "leaf" is formed through an arbitrary abstraction from these individual differences, through forgetting the distinctions; and now it gives rise to the idea that in nature there might be something besides the leaves which would be "leaf" - some kind of original form after which all leaves have been woven, marked, copied, colored, curled, and painted, but by unskilled hands, so that no copy turned out to be a correct, reliable, and faithful image of the original form. Given a program running on one node, how can it tell that a remote node has failed? CA (consistency + availability). An introduction to distributed systems. Granted, "distributed systems" is a enormous topic that no book can cover fully, but I have tried to cover things like: - key papers (Lamport; Fischer, Lynch and Patterson; Chandra and Toueg etc.)