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Fix epoch/term language; Zookeeper -> ZooKeeper #61

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Fix epoch/term language; Zookeeper -> ZooKeeper #61

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4 changes: 2 additions & 2 deletions input/4_replication.md
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Expand Up @@ -211,7 +211,7 @@ Both Paxos and Raft make use of distinct node roles. In particular, they have a

### Epochs

Each period of normal operation in both Paxos and Raft is called an epoch ("term" in Raft). During each epoch only one node is the designated leader (a similar system is [used in Japan](http://en.wikipedia.org/wiki/Japanese_era_name) where era names change upon imperial succession).
Each period of normal operation in Paxos is called an epoch (a "term" in Raft). During each epoch only one node is the designated leader (a similar system is [used in Japan](http://en.wikipedia.org/wiki/Japanese_era_name) where era names change upon imperial succession).

<img src="images/epoch.png" alt="replication" style="max-height: 130px;">

Expand Down Expand Up @@ -295,7 +295,7 @@ Paxos is named after the Greek island of Paxos, and was originally presented by

The issues mostly relate to the fact that Paxos is described in terms of a single round of consensus decision making, but an actual working implementation usually wants to run multiple rounds of consensus efficiently. This has led to the development of many [extensions on the core protocol](http://en.wikipedia.org/wiki/Paxos_algorithm) that anyone interested in building a Paxos-based system still needs to digest. Furthermore, there are additional practical challenges such as how to facilitate cluster membership change.

*ZAB*. ZAB - the Zookeeper Atomic Broadcast protocol is used in Apache Zookeeper. Zookeeper is a system which provides coordination primitives for distributed systems, and is used by many Hadoop-centric distributed systems for coordination (e.g. [HBase](http://hbase.apache.org/), [Storm](http://storm-project.net/), [Kafka](http://kafka.apache.org/)). Zookeeper is basically the open source community's version of Chubby. Technically speaking atomic broadcast is a problem different from pure consensus, but it still falls under the category of partition tolerant algorithms that ensure strong consistency.
*ZAB*. ZAB - the ZooKeeper Atomic Broadcast protocol is used in Apache ZooKeeper. ZooKeeper is a system which provides coordination primitives for distributed systems, and is used by many Hadoop-centric distributed systems for coordination (e.g. [HBase](http://hbase.apache.org/), [Storm](http://storm-project.net/), [Kafka](http://kafka.apache.org/)). ZooKeeper is basically the open source community's version of Chubby. Technically speaking atomic broadcast is a problem different from pure consensus, but it still falls under the category of partition tolerant algorithms that ensure strong consistency.

*Raft*. Raft is a recent (2013) addition to this family of algorithms. It is designed to be easier to teach than Paxos, while providing the same guarantees. In particular, the different parts of the algorithm are more clearly separated and the paper also describes a mechanism for cluster membership change. It has recently seen adoption in [etcd](https://github.com/coreos/etcd) inspired by ZooKeeper.

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