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Thawan Kooburat commented on ZOOKEEPER-1549: -------------------------------------------- I agree that your current solution works in the leader side, but I am not sure how you plan to fix the problem on the learner side. Even if we only need to consider Zap1.0 protocol. The learner need to commit its state (and history) when it receive NEWLEADER packet and send ACK back to the LEADER. However, we cannot write take the snapshot now since it may contain uncommitted state. Are we going to take the snapshot after getting UPTODATE from the leader instead? > Data inconsistency when follower is receiving a DIFF with a dirty snapshot > -------------------------------------------------------------------------- > > Key: ZOOKEEPER-1549 > URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1549 > Project: ZooKeeper > Issue Type: Bug > Components: quorum > Affects Versions: 3.4.3 > Reporter: Jacky007 > Priority: Critical > Attachments: case.patch > > > the trunc code (from ZOOKEEPER-1154?) cannot work correct if the snapshot is > not correct. > here is scenario(similar to 1154): > Initial Condition > 1. Lets say there are three nodes in the ensemble A,B,C with A being the > leader > 2. The current epoch is 7. > 3. For simplicity of the example, lets say zxid is a two digit number, > with epoch being the first digit. > 4. The zxid is 73 > 5. All the nodes have seen the change 73 and have persistently logged it. > Step 1 > Request with zxid 74 is issued. The leader A writes it to the log but there > is a crash of the entire ensemble and B,C never write the change 74 to their > log. > Step 2 > A,B restart, A is elected as the new leader, and A will load data and take a > clean snapshot(change 74 is in it), then send diff to B, but B died before > sync with A. A died later. > Step 3 > B,C restart, A is still down > B,C form the quorum > B is the new leader. Lets say B minCommitLog is 71 and maxCommitLog is 73 > epoch is now 8, zxid is 80 > Request with zxid 81 is successful. On B, minCommitLog is now 71, > maxCommitLog is 81 > Step 4 > A starts up. It applies the change in request with zxid 74 to its in-memory > data tree > A contacts B to registerAsFollower and provides 74 as its ZxId > Since 71<=74<=81, B decides to send A the diff. > Problem: > The problem with the above sequence is that after truncate the log, A will > load the snapshot again which is not correct. > In 3.3 branch, FileTxnSnapLog.restore does not call listener(ZOOKEEPER-874), > the leader will send a snapshot to follower, it will not be a problem. -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators For more information on JIRA, see: http://www.atlassian.com/software/jira