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From: Ted Dunning <ted.dunning@gmail.com>
Date: Tue, 6 Nov 2012 10:29:32 -0800
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 <CAJwFCa2ffPFAN8gRCk6L4Jz0JfsUX1bEiPH7nqZQui1SHOFCpA@mail.gmail.com>
Subject: Re: question about data replication
To: user@zookeeper.apache.org
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Implied by the number of nodes.

On Tue, Nov 6, 2012 at 8:56 AM, Brian Tarbox <briantarbox@gmail.com> wrote:

> Ted,
> Thanks. Is it an actual value I set in zoo.cfg or is it just implied by the
> number of nodes in my cluster?
> Sorry for being dense :-)
>
> Brian
>
>
> On Tue, Nov 6, 2012 at 11:37 AM, Ted Dunning <ted.dunning@gmail.com>
> wrote:
>
> > You specify the MINIMUM number of copies when you define the number of
> > nodes in your ZK cluster.
> >
> > The idea is that ZK requires strong consistency and provides guarantees
> to
> > that effect.  The only way to provide those guarantees is if a majority
> of
> > the ZK cluster agree to and persist all changes.  That is in strong
> > contrast to Cassandra which tries to provide availability instead of
> > consistency.
> >
> > Since ZK requires a majority for every commit, a cluster defined with N
> > nodes will require ceiling((N+1)/2) nodes to commit every change.
> >  Likewise, N is not flexible without some care to make sure that these
> > guarantees are maintained.
> >
> > On Tue, Nov 6, 2012 at 6:50 AM, Brian Tarbox <briantarbox@gmail.com>
> > wrote:
> >
> > > I'm working with both Cassandra and Zookeeper so please excuse me if
> this
> > > is a dumb question but does Zookeeper allow/require me to specify the
> > > number of copies of data (like Cassandra does) or is it simply the case
> > > that if a majority of nodes are up then ALL of my data is available?
> > >
> > > Thanks.  I'm guessing this should be obvious to me but searching the
> > > various docs didn't yield a clear answer.
> > >
> > > Thanks again.
> > >
> > > Brian Tarbox
> > >
> > > --
> > > http://about.me/BrianTarbox
> > >
> >
>
>
>
> --
> http://about.me/BrianTarbox
>

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