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

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

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

Flavio Junqueira updated ZOOKEEPER-876:
---------------------------------------

    Status: Open  (was: Patch Available)

This is a nice catch, Diogo, and the patch looks good to me. I have a few very quick comments:

# Instead of returning a pair of longs in startForwarding, we could simply return maxZxid and read lastProposed directly from the leader object. Doesn't it work?
# The first comment of startForwarding is not saying much. Could you please expand it?
# Could you please explain in the beginning of the test case what it is supposed to be testing? It is for later remembering what the test does.

Good job!



> 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: 3.3.1
>            Reporter: Diogo
>            Assignee: Diogo
>            Priority: Minor
>             Fix For: 3.4.0
>
>         Attachments: 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. (LearnerFollower.java:310)
> 2) if follower is one zxid behind, the check of the interval of committed logs excludes the follower. (LearnerFollower.java:269)
> 3) the bug reported in ZOOKEEPER-874 (commitLogs are empty after recover).

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