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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8964) Provide max TxId when validating in-progress edit log files
Date Thu, 27 Aug 2015 18:47:46 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8964?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14717279#comment-14717279

Colin Patrick McCabe commented on HDFS-8964:

The overall idea looks good.  Rather than special-casing negative values for maxTxId, we can
just pass in {{Long.MAX_VALUE}} in cases where we really don't want a limit.  Of course we
also need to plug this into the relevant places in NameNode and JournalNode.

> Provide max TxId when validating in-progress edit log files
> -----------------------------------------------------------
>                 Key: HDFS-8964
>                 URL: https://issues.apache.org/jira/browse/HDFS-8964
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: journal-node, namenode
>    Affects Versions: 2.7.1
>            Reporter: Zhe Zhang
>            Assignee: Zhe Zhang
>         Attachments: HDFS-8964.00.patch
> NN/JN validates in-progress edit log files in multiple scenarios, via {{EditLogFile#validateLog}}.
The method scans through the edit log file to find the last transaction ID.
> However, an in-progress edit log file could be actively written to, which creates a race
condition and causes incorrect data to be read (and later we attempt to interpret the data
as ops).
> Currently {{validateLog}} is used in 3 places:
> # NN {{getEditsFromTxid}}
> # JN {{getEditLogManifest}}
> # NN/JN {{recoverUnfinalizedSegments}}
> In the first two scenarios we should provide a maximum TxId to validate in the in-progress
file. The 3rd scenario won't cause a race condition because only non-current in-progress edit
log files are validated.
> {{validateLog}} is actually only used with in-progress files, and could use a better
name and Javadoc.

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