[
https://issues.apache.org/jira/browse/ZOOKEEPER-1934?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14028178#comment-14028178
]
Marshall McMullen commented on ZOOKEEPER-1934:
----------------------------------------------
[~michim] - thanks for looking at this issue. I saw the same code you linked to
and agree on the intended behavior. The log message in that block of code is
NOT present.
We did not see /binchanges update to the correct value of 3. It looked to be
stuck at 2. Which really defies explanation.
> Stale data received from sync'd ensemble peer
> ---------------------------------------------
>
> Key: ZOOKEEPER-1934
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1934
> Project: ZooKeeper
> Issue Type: Bug
> Affects Versions: 3.5.0
> Reporter: Marshall McMullen
> Attachments: node1.log, node2.log, node3.log, node4.log, node5.log
>
>
> In our regression testing we encountered an error wherein we were caching a
> value we read from zookeeper and then experienced session loss. We
> subsequently got reconnected to a different zookeeper server. When we tried
> to read the same path from this new zookeeper server we are getting a stale
> value.
> Specifically, we are reading "/binchanges" and originally got back a value of
> "3" from the first server. After we lost connection and reconnected before
> the session timeout, we then read "/binchanges" from the new server and got
> back a value of "2". In our code path we never set this value from 3 to 2. We
> throw an assertion if the value ever goes backwards. Which is how we caught
> this error.
> It's my understanding of the single system image guarantee that this should
> never be allowed. I realize that the single system image guarantee is still
> quorum based and it's certainly possible that a minority of the ensemble may
> have stale data. However, I also believe that each client has to send the
> highest zxid it's seen as part of its connection request to the server. And
> if the server it's connecting to has a smaller zxid than the value the client
> sends, then the connection request should be refused.
> Assuming I have all of that correct, then I'm at a loss for how this
> happened.
> The failure happened around Jun 4 08:13:44. Just before that, at June 4
> 08:13:30 there was a round of leader election. During that round of leader
> election we voted server with id=4 and zxid=0x300001c4c. This then led to a
> new zxid=0x400000001. The new leader sends a diff to all the servers
> including the one we will soon read the stale data from (id=2). Server with
> ID=2's log files also reflect that as of 08:13:43 it was up to date and
> current with an UPTODATE message.
> I'm going to attach log files from all 5 ensemble nodes. I also used
> zktreeutil to dump the database out for the 5 ensemble nodes. I diff'd those,
> and compared them all for correctness. 1 of the nodes (id=2) has a massively
> divergent zktreeutil dump than the other 4 nodes even though it received the
> diff from the new leader.
> In the attachments there are 5 nodes. I will number each log file by it's
> zookeeper id, e.g. node4.log.
--
This message was sent by Atlassian JIRA
(v6.2#6252)
