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From Patrick Hunt <ph...@apache.org>
Subject Re: election recipe
Date Tue, 07 Sep 2010 06:16:45 GMT
Hi Andrei, the answer may not be as simple as that. In the case of "passive
leader" you might want to just wait till you're reconnected before taking
any action. Connection loss indicates that you aren't currently connected to
a server, it doesn't mean that you've lost leadership (if you get expired
that would mean you lost leader). However for "active leader" you might want
to stop acting as leader immed. upon connection loss (given you don't know
if you're the leader any longer). The active vs passive leader distinction
is indicating whether the leader is the one taking the action (active), or
the followers are the ones taking the action (passive). For example in the
active case the leader may be sending out commands to the followers, in the
passive case the leader might be getting requests from the followers. In the
first case you want to stop as soon as you are not sure you're the leader,
in the passive case the followers will stop talking to you on their own if
leadership change does take place.

Patrick

On Sat, Sep 4, 2010 at 11:16 AM, Andrei Savu <savu.andrei@gmail.com> wrote:

> You should also be careful how you handle connection loss events. The
> leader should suspend itself and re-run the election process when the
> connection is reestablished.
>
> On Sat, Sep 4, 2010 at 8:37 AM, Mahadev Konar <mahadev@yahoo-inc.com>
> wrote:
> > Hi Eric,
> >  As Ted and you yourself mentioned its mostly to avoid herd affect.  A
> herd
> > affect would usually mean 1000¹s of client notified of some change and
> would
> > try creating the same node on notification.  With just 10¹s of clients
> you
> > don¹t need to worry abt this herd effect at all.
> >
> > Thanks
> > mahadev
> >
> >
> > On 9/2/10 3:40 PM, "Ted Dunning" <ted.dunning@gmail.com> wrote:
> >
> >> You are correct that this simpler recipe will work for smaller
> populations
> >> and correct that the complications are to avoid the herd effect.
> >>
> >>
> >>
> >> On Thu, Sep 2, 2010 at 12:55 PM, Eric van Orsouw
> >> <eric.van.orsouw@gmail.com>wrote:
> >>
> >>> Hi there,
> >>>
> >>>
> >>>
> >>> I would like to use zookeeper to implement an election scheme.
> >>>
> >>> There is a recipe on the homepage, but it is relatively complex.
> >>>
> >>> I was wondering what was wrong with the following pseudo code;
> >>>
> >>>
> >>>
> >>> forever {
> >>>
> >>>    zookeeper.create -e /election <my_ip_address>
> >>>
> >>>    if creation succeeded then {
> >>>
> >>>        // do the leader thing
> >>>
> >>>    } else {
> >>>
> >>>        // wait for change in /election using watcher mechanism
> >>>
> >>>    }
> >>>
> >>> }
> >>>
> >>>
> >>>
> >>> My assumption is that the recipe is more elaborate to the eliminate the
> >>> flood of requests if the leader falls away.
> >>>
> >>> But if there are only a handful of leader-candidates ,than that should
> not
> >>> be a problem.
> >>>
> >>>
> >>>
> >>> Is this correct, or am I missing out on something.
> >>>
> >>>
> >>>
> >>> Thanks,
> >>>
> >>> Eric
> >>>
> >>>
> >>>
> >>>
> >>
> >
> >
>
>
>
> --
> Andrei Savu -- http://www.andreisavu.ro/
>

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