[jira] [Commented] (ZOOKEEPER-2033) zookeeper follower fails to start after a restart immediately following a new epoch

["Flavio Junqueira (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2033?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14728269#comment-14728269 ] 

Flavio Junqueira commented on ZOOKEEPER-2033:
---------------------------------------------

I believe the real issue is that proposals should have be empty in this case and it isn't. It seems that the leader is populating committedLog and generating a snapshot by the end of the synchronization phase, but it is not updating the committedLog list accordingly. 

I don't know if [~asadpanda] is still interested in finishing this up after such a long time, but I can give it a shot otherwise. 

> zookeeper follower fails to start after a restart immediately following a new epoch
> -----------------------------------------------------------------------------------
>
>                 Key: ZOOKEEPER-2033
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2033
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: quorum
>    Affects Versions: 3.4.6
>            Reporter: Asad Saeed
>            Assignee: Asad Saeed
>             Fix For: 3.4.7
>
>         Attachments: ZOOKEEPER-2033-3.4.patch, ZOOKEEPER-2033.patch
>
>
> The following issue was seen when adding a new node to a zookeeper cluster.
> Reproduction steps
> 1. Create a 2 node ensemble. Write some keys.
> 2. Add another node to the ensemble, by modifying the config. Restarting entire cluster.
> 3. Restart the new node before writing any new keys.
> What occurs is that the new node gets a SNAP from the newly elected leader, since it is too far behind. The zxid for this snapshot is from the new epoch but that is not in the committed log cache.
> On restart of this new node. The follower sends the new epoch zxid. The leader looks at it's maxCommitted logs, and sees that it is not the newest epoch, and therefore sends a TRUNC.
> The follower sees the TRUNC but it only has a snapshot, so it cannot truncate!



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