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From "Michael Han (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (ZOOKEEPER-2418) txnlog diff sync can skip sending some transactions to followers
Date Wed, 03 Jul 2019 18:55:00 GMT

     [ https://issues.apache.org/jira/browse/ZOOKEEPER-2418?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Michael Han resolved ZOOKEEPER-2418.
------------------------------------
       Resolution: Fixed
    Fix Version/s: 3.6.0

Issue resolved by pull request 972
[https://github.com/apache/zookeeper/pull/972]

> txnlog diff sync can skip sending some transactions to followers
> ----------------------------------------------------------------
>
>                 Key: ZOOKEEPER-2418
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2418
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: server
>    Affects Versions: 3.5.1
>            Reporter: Nicholas Wolchko
>            Assignee: Brian Nixon
>            Priority: Critical
>              Labels: pull-request-available
>             Fix For: 3.6.0
>
>   Original Estimate: 168h
>          Time Spent: 1.5h
>  Remaining Estimate: 166.5h
>
> If the leader is having disk issues so that its on disk txnlog is behind the in memory
commit log, it will send a DIFF that is missing the transactions in between the two.
> Example:
> There are 5 hosts in the cluster. 1 is the leader. 5 is disconnected.
> We commit up to zxid 1000.
> At zxid 450, the leader's disk stalls, but we still commit transactions because 2,3,4
are up and acking writes.
> At zxid 1000, the txnlog on the leader has 1-450 and the commit log has 500-1000.
> Then host 5 regains its connection to the cluster and syncs with the leader. It will
receive a DIFF containing zxids 1-450 and 500-1000.
> This is because queueCommittedProposals in the LearnerHandler just queues everything
within its zxid range. It doesn't give an error if there is a gap between peerLastZxid and
the iterator it is queueing from.



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