Home | About | Sematext search-lucene.com search-hadoop.com
NEW: Monitor These Apps!
elasticsearch, apache solr, apache hbase, hadoop, redis, casssandra, amazon cloudwatch, mysql, memcached, apache kafka, apache zookeeper, apache storm, ubuntu, centOS, red hat, debian, puppet labs, java, senseiDB
 Search Hadoop and all its subprojects:

Switch to Threaded View
Zookeeper >> mail # user >> Possibility / consequences of having multiple elected leaders


Copy link to this message
-
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
>  
NEW: Monitor These Apps!
elasticsearch, apache solr, apache hbase, hadoop, redis, casssandra, amazon cloudwatch, mysql, memcached, apache kafka, apache zookeeper, apache storm, ubuntu, centOS, red hat, debian, puppet labs, java, senseiDB