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Date: Thu, 20 Sep 2012 05:58:09 +1100 (NCT)
From: "Todd Lipcon (JIRA)" <jira@apache.org>
To: hdfs-dev@hadoop.apache.org
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Subject: [jira] [Resolved] (HDFS-3955) QJM: Make acceptRecovery() atomic
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     [ https://issues.apache.org/jira/browse/HDFS-3955?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Todd Lipcon resolved HDFS-3955.
-------------------------------

       Resolution: Fixed
    Fix Version/s: QuorumJournalManager (HDFS-3077)
     Hadoop Flags: Reviewed
    
> QJM: Make acceptRecovery() atomic
> ---------------------------------
>
>                 Key: HDFS-3955
>                 URL: https://issues.apache.org/jira/browse/HDFS-3955
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: ha
>    Affects Versions: QuorumJournalManager (HDFS-3077)
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>             Fix For: QuorumJournalManager (HDFS-3077)
>
>         Attachments: hdfs-3955.txt
>
>
> Per one of the TODOs in Journal.java, there is currently a lack of atomicity in the {{acceptRecovery()}} code path. In particular, we have the following actions executed non-atomically:
> - Download a new edits_inprogress_N from some other node
> - Persist the paxos recovery file to disk.
> If the JN crashes between these two steps, then we may be left in the state whereby the edits_inprogress file has different data than the Paxos data left over on the disk from a previous recovery attempt. This causes the next {{prepareRecovery()}} to fail with an AssertionError.
> I discovered this by randomly injecting a fault between the two steps, and then running the randomized fault test on a cluster. This resulted in some AssertionErrors in the test logs.

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