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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ZOOKEEPER-2846) Leader follower sync with on disk txns can possibly leads to data inconsistency
Date Tue, 18 Jul 2017 19:50:00 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2846?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16092075#comment-16092075
] 

Hadoop QA commented on ZOOKEEPER-2846:
--------------------------------------

-1 overall.  GitHub Pull Request  Build
      

    +1 @author.  The patch does not contain any @author tags.

    +1 tests included.  The patch appears to include 3 new or modified tests.

    +1 javadoc.  The javadoc tool did not generate any warning messages.

    +1 javac.  The applied patch does not increase the total number of javac compiler warnings.

    +1 findbugs.  The patch does not introduce any new Findbugs (version 3.0.1) warnings.

    +1 release audit.  The applied patch does not increase the total number of release audit
warnings.

    -1 core tests.  The patch failed core unit tests.

    +1 contrib tests.  The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-ZOOKEEPER-github-pr-build/887//testReport/
Findbugs warnings: https://builds.apache.org/job/PreCommit-ZOOKEEPER-github-pr-build/887//artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Console output: https://builds.apache.org/job/PreCommit-ZOOKEEPER-github-pr-build/887//console

This message is automatically generated.

> Leader follower sync with on disk txns can possibly leads to data inconsistency
> -------------------------------------------------------------------------------
>
>                 Key: ZOOKEEPER-2846
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2846
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: quorum
>    Affects Versions: 3.4.10, 3.5.3, 3.6.0
>            Reporter: Fangmin Lv
>            Priority: Critical
>
> On disk txn sync could cause data inconsistency if the current leader just had a snap
sync before it became leader, and then having diff sync with its followers may synced the
txns gap on disk. Here is scenario: 
> Let's say S0 - S3 are followers, and S4 is leader at the beginning:
> 1. Stop S2 and send one more request
> 2. Stop S3 and send more requests to the quorum to let S3 have a snap sync with S4 when
it started up
> 3. Stop S4 and S3 became the new leader
> 4. Start S2 and had a diff sync with S3, now there are gaps in S2
> Attached the test case to verify the issue. Currently, there is no efficient way to check
the gap in txn files is a real gap or due to Epoch change. We need to add that support, but
before that, it would be safer to disable the on disk txn leader-follower sync.



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