[jira] [Resolved] (ZOOKEEPER-876) Unnecessary snapshot transfers between new leader and followers

["Thawan Kooburat (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ZOOKEEPER-876?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Thawan Kooburat resolved ZOOKEEPER-876.
---------------------------------------

    Resolution: Fixed

ZOOKEEPER-1413 address all of the issues mentioned in the description. However, there is one corner case (used by the unit test in this patch) which is not covered by ZOOKEEPER-1413 where the learner tries to sync with leader with no txnlog. 
                
> Unnecessary snapshot transfers between new leader and followers
> ---------------------------------------------------------------
>
>                 Key: ZOOKEEPER-876
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-876
>             Project: ZooKeeper
>          Issue Type: Bug
>    Affects Versions: 3.4.0
>            Reporter: Diogo
>            Assignee: Diogo
>            Priority: Minor
>             Fix For: 3.5.0
>
>         Attachments: second_case.patch, second_case.txt, TEST-org.apache.zookeeper.test.FollowerResyncConcurrencyTest.txt, ZOOKEEPER-876.patch
>
>
> When starting a new leadership, unnecessary snapshot transfers happen between new leader and followers. This is so because of multiple small bugs. 
> 1) the comparison of zxids is done based on a new proposal, instead of the last logged zxid. (LearnerHandler.java ~ 297)
> 2) if follower is one zxid behind, the check of the interval of committed logs excludes the follower. (LearnerHandler.java ~ 277)
> 3) the bug reported in ZOOKEEPER-874 (commitLogs are empty after recover).

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