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From Scott Carey <sc...@richrelevance.com>
Subject Re: Leader Elections
Date Mon, 20 Jul 2009 18:00:19 GMT
Observers would be awesome especially with a couple enhancements / extensions:

An option for the observers to enter a special state if the WAN link goes down to the "master"
cluster.  A read-only option would be great.
However, allowing certain types of writes to continue on a limited basis would be highly valuable
as well.  An observer could "own" a special node and its subnodes.  Only these subnodes would
be writable by the observer when there was a session break to the master cluster, and the
master cluster would take all the changes when the link is reestablished.  Essentially, it
is a portion of the hierarchy that is writable only by a specitfic observer, and read-only
for others.
The purpose of this would be for when the WAN link goes down to the "master" ZKs for certain
types of use cases - status updates or other changes local to the observer that are strictly
read-only outside the Observer's 'realm'.

On 7/19/09 12:16 PM, "Henry Robinson" <henry@cloudera.com> wrote:

You can. See ZOOKEEPER-368 - at first glance it sounds like observers will
be a good fit for your requirements.

Do bear in mind that the patch on the jira is only for discussion purposes;
I would not consider it currently fit for production use. I hope to put up a
much better patch this week.


On Sat, Jul 18, 2009 at 7:38 PM, Ted Dunning <ted.dunning@gmail.com> wrote:

> Can you submit updates via an observer?
> On Sat, Jul 18, 2009 at 6:38 AM, Flavio Junqueira <fpj@yahoo-inc.com>
> wrote:
> > 2- Observers: you could have one computing center containing an ensemble
> > and observers around the edge just learning committed values.
> --
> Ted Dunning, CTO
> DeepDyve

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