[jira] [Comment Edited] (ZOOKEEPER-4005) Zookeeper will not sync snapshot while get DIFF and cause start failed.

["pengWei Dou (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-4005?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17235384#comment-17235384 ] 

pengWei Dou edited comment on ZOOKEEPER-4005 at 11/19/20, 12:45 PM:
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[~hanm] , yes, we can disable  check snapshot during upgrade,  but we should't always disable it, that means we need to modify configuration again while upgrade completed.   so i think we can do this as follow:
{code:java}
// code placeholder


if (qp.getType() == Leader.DIFF) {
    LOG.info("Getting a diff from the leader 0x{}", Long.toHexString(qp.getZxid()));
    //add check whether snapshot file  exist
    if (zk.existSnapshot()) {
        snapshotNeeded = false;
    }
}
{code}


was (Author: doudou):
[~hanm] , yes, we can disable  check snapshot during upgrade,  but we should't always disable it, that means we need to modify configuration again while upgrade completed.   so i think we can do this as follow:
{code:java}
// code placeholder


if (qp.getType() == Leader.DIFF) {
    LOG.info("Getting a diff from the leader 0x{}", Long.toHexString(qp.getZxid()));
    //add check whether snapshot file exist
    snapshotNeeded = false;
}
{code}

> Zookeeper will not sync snapshot while get DIFF and cause start failed.
> -----------------------------------------------------------------------
>
>                 Key: ZOOKEEPER-4005
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-4005
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: server
>    Affects Versions: 3.5.1, 3.5.6
>            Reporter: pengWei Dou
>            Priority: Major
>         Attachments: zookeeper-server.log
>
>
> The  version 3.5.1 of ZK does not detect whether the snapshot file exists or not. However, the snapshot file detection is added in the subsequent version. When I tested the upgrade from 3.5.1 to 3.5.6, I found that after the completion of ZK election, One of the ZK node has an error in the following phase due to some network reasons, and then it will receive a diff reply. At this time,  both snapshotNeeded and isPreZAB1_0 （   Learner#syncWithLeader(long newLeaderZxid)  ）are assigned to false.  So, none of snapshot file will be generated but a log file, which will cause the startup failure after the upgrade. 
>  
>  
>  



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