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Date: Mon, 23 Jan 2017 04:19:27 +0000 (UTC)
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Subject: [jira] [Commented] (ZOOKEEPER-2574) PurgeTxnLog can inadvertently
 delete required txn log files
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archived-at: Mon, 23 Jan 2017 04:19:33 -0000


    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2574?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15833883#comment-15833883 ] 

ASF GitHub Bot commented on ZOOKEEPER-2574:
-------------------------------------------

Github user abhishekrai commented on the issue:

    https://github.com/apache/zookeeper/pull/111
  
    Thanks @hanm!


> PurgeTxnLog can inadvertently delete required txn log files
> -----------------------------------------------------------
>
>                 Key: ZOOKEEPER-2574
>                 URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2574
>             Project: ZooKeeper
>          Issue Type: Bug
>          Components: server
>    Affects Versions: 3.4.7, 3.4.8, 3.5.0, 3.5.1, 3.5.2
>         Environment: Zookeeper 3.4.8, standalone, and 3-server quorum
>            Reporter: Abhishek Rai
>            Assignee: Abhishek Rai
>             Fix For: 3.4.10, 3.5.3, 3.6.0
>
>         Attachments: ZOOKEEPER-2574.2.patch, ZOOKEEPER-2574.3.patch, ZOOKEEPER-2574.4.patch, ZOOKEEPER-2574.5.patch, ZOOKEEPER-2574.6.patch, ZOOKEEPER-2574.patch
>
>
> As part of the fix for ZOOKEEPER-1797, the call to FileTxnSnapLog.getSnapshotLogs() was removed from PurgeTxnLog.java.  As a result, some old-looking but required txn log files can be deleted, resulting in data corruption or loss.
> For example, consider the following:
> 1. Configuration:
> autopurge.snapRetainCount=3
> 2. Following files exist:
> log.100 spans transactions from zxid=100 till zxid=140 (inclusive)
> snapshot.110 - snapshot as of zxid=110
> snapshot.120 - snapshot as of zxid=120
> snapshot.130 - snapshot as of zxid=130
> Above scenario is possible when snapshotting has happened multiple times but without accompanying log rollover, which is possible if the server was running as a learner.
> 3. PurgeTxnLog retains all snapshots but deletes log.100 because its zxid is older than the zxid of the oldest snapshot (110).  This results in loss of transactions in the range 131-140.
> Before the fix for ZOOKEEPER-1797, this was avoided by the call to FileTxnSnapLog.getSnapshotLogs() which finds and retains the newest txn log file with starting zxid < oldest retained snapshot's highest zxid.


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