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From: Camille Fournier <camille@apache.org>
Date: Fri, 3 Jun 2016 16:30:05 -0400
Message-ID: <CABWqe2Zfe7TYMJjwQUKrzhBnt0Z=Hvr-L-V8AKzB90Z5MP=q3w@mail.gmail.com>
Subject: Re: zookeeper deployment strategy for multi data centers
To: "user@zookeeper.apache.org" <user@zookeeper.apache.org>
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archived-at: Fri, 03 Jun 2016 20:30:08 -0000

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2 servers is the same as 1 server wrt fault tolerance, so yes, you are
correct. If they want fault tolerance, they have to run 3 (or more).

On Fri, Jun 3, 2016 at 4:25 PM, Shawn Heisey <apache@elyograg.org> wrote:

> On 6/3/2016 1:44 PM, Nomar Morado wrote:
> > Is there any settings to override the quorum rule? Would you know the
> > rationale behind it? Ideally, you will want to operate the application
> > even if at least one data center is up.
>
> I do not know if the quorum rule can be overridden, or whether your
> application can tell the difference between a loss of quorum and
> zookeeper going down entirely.  I really don't know anything about
> zookeeper client code or zookeeper internals.
>
> From what I understand, majority quorum is the only way to be
> *completely* sure that cluster software like SolrCloud or your
> application can handle write operations with confidence that they are
> applied correctly.  If you lose quorum, which will happen if only one DC
> is operational, then your application should go read-only.  This is what
> SolrCloud does.
>
> I am a committer on the Apache Solr project, and Solr uses zookeeper
> when it is running in SolrCloud mode.  The cloud code is handled by
> other people -- I don't know much about it.
>
> I joined this list because I wanted to have the ZK devs include a
> clarification in zookeeper documentation -- oddly enough, related to the
> very thing we are discussing.  I wanted to be sure that the
> documentation explicitly mentioned that three serversare required for a
> fault-tolerant setup.  Some SolrCloud users don't want to accept this as
> a fact, and believe that two servers should be enough.
>
> Thanks,
> Shawn
>
>

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