Hi Charity, This is certainly not expected. It would be very useful if you could provide us with as much information about your issue as possible. I would suggest that either you create a new jira and link it to ZOOKEEPER-335, or that you add to 335 directly.

We'll be looking further into why you have seen this problem and working on a fix.


On Jun 2, 2010, at 10:32 PM, Charity Majors wrote:

Thanks. That worked for me. I'm a little confused about why it threw the entire cluster into an unusable state, though.

I said before that we restarted all three nodes, but tracing back, we actually didn't. The zookeeper cluster was refusing all connections until we restarted node one. But once node one had been dropped from the cluster, the other two nodes formed a quorum and started responding to queries on their own.

Is that expected as well? I didn't see it in ZOOKEEPER-335, so thought I'd mention it.

On Jun 2, 2010, at 11:49 AM, Patrick Hunt wrote:

Hi Charity, unfortunately this is a known issue not specific to 3.3 that
we are working to address. See this thread for some background:


I've raised the JIRA level to "blocker" to ensure we address this asap.

As Ted suggested you can remove the datadir -- only on the effected
server -- and then restart it. That should resolve the issue (the server
will d/l a snapshot of the current db from the leader).


On 06/02/2010 11:11 AM, Charity Majors wrote:
I upgraded my zookeeper cluster last week from 3.2.1 to 3.3.1, in an attempt to get away from a client bug that was crashing my backend services.

Unfortunately, this morning I had a server crash, and it brought down my entire cluster. I don't have the logs leading up to the crash, because -- argghffbuggle -- log4j wasn't set up correctly. But I restarted all three nodes, and odes two and three came back up and formed a quorum.

Node one, meanwhile, does this:

2010-06-02 17:04:56,446 - INFO [QuorumPeer:/ 0:0:0:0:0:0:0:0:2181:quorump...@620] - LOOKING 2010-06-02 17:04:56,446 - INFO [QuorumPeer:/ 0:0:0:0:0:0:0:0:2181:files...@82] - Reading snapshot /services/ zookeeper/data/zookeeper/version-2/snapshot.a00000045 2010-06-02 17:04:56,476 - INFO [QuorumPeer:/ 0:0:0:0:0:0:0:0:2181:fastleaderelect...@649] - New election. My id = 1, Proposed zxid = 47244640287 2010-06-02 17:04:56,486 - INFO [QuorumPeer:/ 0:0:0:0:0:0:0:0:2181:fastleaderelect...@689] - Notification: 1, 47244640287, 4, 1, LOOKING, LOOKING, 1 2010-06-02 17:04:56,486 - INFO [QuorumPeer:/ 0:0:0:0:0:0:0:0:2181:fastleaderelect...@799] - Notification: 3, 38654707048, 3, 1, LOOKING, LEADING, 3 2010-06-02 17:04:56,486 - INFO [QuorumPeer:/ 0:0:0:0:0:0:0:0:2181:fastleaderelect...@799] - Notification: 3, 38654707048, 3, 1, LOOKING, FOLLOWING, 2 2010-06-02 17:04:56,486 - INFO [QuorumPeer:/ 0:0:0:0:0:0:0:0:2181:quorump...@642] - FOLLOWING 2010-06-02 17:04:56,486 - INFO [QuorumPeer:/ 0:0:0:0:0:0:0:0:2181:zookeeperser...@151] - Created server with tickTime 2000 minSessionTimeout 4000 maxSessionTimeout 40000 datadir /services/zookeeper/data/zookeeper/version-2 snapdir / services/zookeeper/data/zookeeper/version-2 2010-06-02 17:04:56,486 - FATAL [QuorumPeer:/ 0:0:0:0:0:0:0:0:2181:follo...@71] - Leader epoch a is less than our epoch b 2010-06-02 17:04:56,486 - WARN [QuorumPeer:/ 0:0:0:0:0:0:0:0:2181:follo...@82] - Exception when following the leader
java.io.IOException: Error: Epoch of leader is lower
at org .apache .zookeeper.server.quorum.Follower.followLeader(Follower.java:73) at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java: 644) 2010-06-02 17:04:56,486 - INFO [QuorumPeer:/ 0:0:0:0:0:0:0:0:2181:follo...@166] - shutdown called
java.lang.Exception: shutdown Follower
at org.apache.zookeeper.server.quorum.Follower.shutdown(Follower.java: 166) at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java: 648)

All I can find is this, http://www.mail-archive.com/zookeeper-comm...@hadoop.apache.org/msg00449.html , which implies that this state should never happen.

Any suggestions? If it happens again, I'll just have to roll everything back to 3.2.1 and live with the client crashes.

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