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 <shra...@yahoo-inc.com> 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:ted.dunn...@gmail.com] > Sent: Wednesday, March 07, 2012 4:55 PM > To: Alexander Shraer > Cc: user@zookeeper.apache.org > 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 <shra...@yahoo-inc.com> > 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 >
