Hi, Zookeeper is all about a shared state called a consensus. So everything that it is at its core is providing any means of joining a group of servers and elect a leader and share information that result in a predictable shared state that all servers agree on.
The most popular consensus algorithm is the Raft algorithm: https://ramcloud.stanford.edu/*raft*.pdf. Reading this paper should clarify most of your confusion regarding what Zookeeper achieves at its very core. Cheers, Martin (Kersten) 2015-08-30 17:47 GMT+02:00 Prabhjot Bharaj <[email protected]>: > Hello Folks, > > I am going through zookeeper internals described here: > http://zookeeper.apache.org/doc/r3.4.6/zookeeperInternals.html > > I have some very basic doubts in understanding the Gurantees - *Reliable > delivery, **Total order *and *Causal order* > > 1. I do not understand the term - 'delivery' and 'order' in these sections. > a) Delivery - Does 'delivery' refer to delivery of messages from server > to server or server to client ? > b) Order - As per this link: > https://cwiki.apache.org/confluence/display/ZOOKEEPER/Zab+vs.+Paxos, state > updates must be ordered - What kind of state updates are these ? Does the > term - 'order' in this link and the one shared in the top of this email > have the same meaning ? > > 2. *'**If a message, m, is delivered by one server, it will be eventually > delivered by all servers.'* - delivered <from what> <to what> ? > > 3. If a and b are delivered messages, either a will be delivered before b > or b will be delivered before a -- dont really understand what this means ! > > 4. the terms sender - Does sender classify as one of the zookeeper servers > in the cluster or the client ? > > > Request you to share your knowledge on my doubts so I can learn more on the > internals and be able to use zookeeper effectively > > Thanks, > Prabhjot >
