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From Todd Nine <t...@spidertracks.co.nz>
Subject Re: What roles do "even" nodes play in the ensamble
Date Thu, 26 Aug 2010 04:01:33 GMT
Thanks Dave.  I've been using Cassandra, so I'm trying to get my head
around the configuration/operational differences with ZK.  You state
that using 4 would actually decrease my reliability.  Can you explain
that further?  I was under the impression that a 4th node would act as a
non voting read only node until one of the other 3 fails.  I thought
that this extra node would give me some breathing room by allowing any
node to fail and still have 3 voting nodes.  Is this not the case?



On Wed, 2010-08-25 at 21:13 -0600, Ted Dunning wrote:

> Just use 3 nodes.  Life will be better.
> You can configure the fourth node in the event of one of the first
> three failing and bring it on line.  Then you can re-configure and
> restart each of the others one at a time.  This gives you flexibility
> because you have 4 nodes, but doesn't decrease your reliability the
> way that using a four node cluster would.  If you need to do
> maintenance on one node, just configure that node out as if it had
> failed.
> On Wed, Aug 25, 2010 at 4:26 PM, Dave Wright <wrightd@gmail.com>
> wrote:
>         You can certainly serve more reads with a 4th node, but I'm
>         not sure
>         what you mean by "it won't have a voting role". It still
>         participates
>         in voting for leaders as do all non-observers regardless of
>         whether it
>         is an even or odd number. With zookeeper there is no voting on
>         each
>         transaction, only leader changes.
>         -Dave Wright
>         On Wed, Aug 25, 2010 at 6:22 PM, Todd Nine
>         <todd@spidertracks.co.nz> wrote:
>         > Do I get any read performance increase (similar to an
>         observer) since
>         > the node will not have a voting role?
>         >
>         >

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