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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ZOOKEEPER-2574) PurgeTxnLog can inadvertently delete required txn log files
Date Mon, 23 Jan 2017 01:30:27 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-2574?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15833791#comment-15833791

Hadoop QA commented on ZOOKEEPER-2574:

-1 overall.  Here are the results of testing the latest attachment 
  against trunk revision 762f4af65bb1056a582a6f36183a9e28fe0ccab8.

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

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

    -1 patch.  The patch command could not apply the patch.

Console output: https://builds.apache.org/job/PreCommit-ZOOKEEPER-Build/3565//console

This message is automatically generated.

> 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
> 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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