Implied by the number of nodes. On Tue, Nov 6, 2012 at 8:56 AM, Brian Tarbox <[email protected]> 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 <[email protected]> > 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 <[email protected]> > > 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 >
