Flavio Paiva Junqueira commented on ZOOKEEPER-261:

I think that currently the value of last zxid is initially -1, so discarding 
votes with zxid -1 may create a problem when starting a new instance of the 
service. I guess you'll say that we can use -2... :-)

> Reinitialized servers should not participate in leader election
> ---------------------------------------------------------------
>                 Key: ZOOKEEPER-261
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-261
>             Project: Zookeeper
>          Issue Type: Improvement
>          Components: leaderElection, quorum
>            Reporter: Benjamin Reed
> A server that has lost its data should not participate in leader election 
> until it has resynced with a leader. Our leader election algorithm and 
> NEW_LEADER commit assumes that the followers voting on a leader have not lost 
> any of their data. We should have a flag in the data directory saying whether 
> or not the data is preserved so that the the flag will be cleared if the data 
> is ever cleared.
> Here is the problematic scenario: you have have ensemble of machines A, B, 
> and C. C is down. the last transaction seen by C is z. a transaction, z+1, is 
> committed on A and B. Now there is a power outage. B's data gets 
> reinitialized. when power comes back up, B and C comes up, but A does not. C 
> will be elected leader and transaction z+1 is lost. (note, this can happen 
> even if all three machines are up and C just responds quickly. in that case C 
> would tell A to truncate z+1 from its log.) in theory we haven't violated our 
> 2f+1 guarantee, since A is failed and B still hasn't recovered from failure, 
> but it would be nice if when we don't have quorum that system stops working 
> rather than works incorrectly if we lose quorum.

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