[jira] [Updated] (ZOOKEEPER-3972) Convergence fail when a follower tries to resync with a leader having incomplete commitlog

["anaud (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ZOOKEEPER-3972?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

anaud updated ZOOKEEPER-3972:
-----------------------------
    Attachment: zookeeper-testResyncWithLeaderHavingIncompleteCommitlog.patch

> Convergence fail when a follower tries to resync with a leader having incomplete commitlog
> ------------------------------------------------------------------------------------------
>
>                 Key: ZOOKEEPER-3972
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3972
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: server
>    Affects Versions: 3.5.8
>            Reporter: anaud
>            Priority: Major
>         Attachments: zookeeper-testResyncWithLeaderHavingIncompleteCommitlog.patch
>
>
> It is possible that a leader may have incomplete commitlog because it resync'ed with the old leader via SNAPSHOT replication.
> Then, a follower may try to resync with the leader, but because there may be some transactions the follower missed earlier and the leader does not have in its commitlog.
> They decided to use txnlog + commitlog to resync. However, this will lead to convergence failure because the leader does not send the missing transactions that are not in its commitlog.
> Here is the abstract step to reproduce the bug, and I attached the patch with the test case that can reproduce the bug.
> Initially, node A,B,C are all sync'ed.
> 1. Node A crashes; setData 0x11 on B and C
> 2. Node B and C crash
> 3. Node A and B restart
> 4. Node A crashes; setData 0x21 on B
> 5. Node B crashes
> 6. Node B and C restart
> 7. Node C crashes; setData 0x32 on B
> 8. Node A and C restart
> 9. Node B restarts
> At step 6, C is a follower getting a snapshot from B, and C does not have the transaction 0x21 in its commitlog (only in the snapshot).
> At step 8, C is the leader which does not have 0x21 in its commitlog, which A never gets.
> In the end, 0x21 only exists on B and C, but not on A.
>  



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