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Zookeeper, mail # user - Possibility / consequences of having multiple elected leaders


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Scott Lindner 2012-03-07, 17:48
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Ted Dunning 2012-03-07, 18:59
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Alexander Shraer 2012-03-08, 00:07
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Ted Dunning 2012-03-08, 00:55
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Alexander Shraer 2012-03-08, 03:08
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Ted Dunning 2012-03-08, 08:31
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Alexander Shraer 2012-03-08, 23:09
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Re: Possibility / consequences of having multiple elected leaders
Ted Dunning 2012-03-08, 23:12
Exactly.

On Thu, Mar 8, 2012 at 3:09 PM, Alexander Shraer <[EMAIL PROTECTED]>wrote:

> Thanks Ted, I can see your point. We use TCP connections and we do the
> epoch check at the beginning of the protocol, so ****
>
> a message from an old leader cannot just resurface. ****
>
> ** **
>
> Alex****
>
> ** **
>
> *From:* Ted Dunning [mailto:[EMAIL PROTECTED]]
> *Sent:* Thursday, March 08, 2012 12:32 AM
>
> *To:* Alexander Shraer
> *Cc:* [EMAIL PROTECTED]
> *Subject:* Re: Possibility / consequences of having multiple elected
> leaders****
>
> ** **
>
> The whole point of the zab protocol is to ensure that only one elected
> leader can exist at one time.  Since a quorum has to commit to supporting
> any leader there can't be two leaders. Furthermore each change of
> leadership increments the epoch and that increment had to be committed on a
> majority of node. That means that only one leader can exist in the latest
> epoch. Since the latest epoch is, by definition, acknowledged by a majority
> of nodes, an old leader cannot resurface as a pretender to the throne.
>
> Sent from my iPhone****
>
>
> On Mar 7, 2012, at 7:08 PM, Alexander Shraer <[EMAIL PROTECTED]>
> wrote:****
>
> I’ve been wondering about this for a while, and suspect that this check
> doesn’t exist in the code… but I may be wrong.****
>
>  ****
>
> *From:* Ted Dunning [mailto:[EMAIL PROTECTED]]
> *Sent:* Wednesday, March 07, 2012 4:55 PM
> *To:* Alexander Shraer
> *Cc:* [EMAIL PROTECTED]
> *Subject:* Re: Possibility / consequences of having multiple elected
> leaders****
>
>  ****
>
> Not off the cuff and I have to run away right now.****
>
>  ****
>
> On Wed, Mar 7, 2012 at 4:07 PM, Alexander Shraer <[EMAIL PROTECTED]>
> wrote:****
>
> > Such a commit will be rejected due to an old epoch.
>
> Ted, can you please point me to the place in the code where this check is
> performed ?
>
> Thanks a lot,
> Alex****
>
>  ****
>
>