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 <CANXk_5nR3Rdg_p5gcbZAmJ8uX=_nEqoWzdkUcott-5JVfpFHrA@mail.gmail.com>
Date: Sun, 30 Aug 2015 19:20:29 +0200
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 <CAC+w5b1Hm2jTR8j_=c144nhn_ooBK_eqFwGiL++VcOeYtuitEQ@mail.gmail.com>
Subject: Re: Doubt in Atomic Broadcast
From: Martin Kersten <martin.kersten.mk@gmail.com>
To: user@zookeeper.apache.org
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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 <prabhbharaj@gmail.com>:

> 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
>

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