Ok, I think this is possible.
So here is what happens currently. This has been a long standing bug and
should be fixed in 3.4
https://issues.apache.org/jira/browse/ZOOKEEPER-335
A newly elected leader currently doesn't log the new leader transaction to
its database
In your case, the follower (the 3rd server) did log it but the leader never
did. Now when you brought up the 3rd server it had the transaction log
present but the leader did not have that. In that case the 3rd server cried
fowl and shut down.
Removing the DB is totally fine. For now, we should update our docs on 3.3
and mention that this problem might occur during upgrade and fix it in 3.4.
Thanks for bringing it up Ted.
Thanks
mahadev
On 4/20/10 2:14 PM, Ted Dunning ted.dunn...@gmail.com wrote:
We have just done an upgrade of ZK to 3.3.0. Previous to this, ZK has been
up for about a year with no problems.
On two nodes, we killed the previous instance and started the 3.3.0
instance. The first node was a follower and the second a leader.
All went according to plan and no clients seemed to notice anything. The
stat command showed connections moving around as expected and all other
indicators were normal.
When we did the third node, we saw this in the log:
2010-04-20 14:07:49,010 - FATAL [QuorumPeer:/0.0.0.0:2181:follo...@71] -
Leader epoch 18 is less than our epoch 19
The third node refused all connections.
We brought down the third node, wiped away its snapshot, restarted and it
joined without complaint. Note that the third node
was originally a follower and had never been a leader during the upgrade
process.
Does anybody know why this happened?
We are fully upgraded and there was no interruption to normal service, but
this seems strange.
