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From "Andrew Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4300) TransferFsImage.downloadEditsToStorage should use a tmp file for destination
Date Tue, 09 Apr 2013 22:56:16 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4300?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13627223#comment-13627223
] 

Andrew Wang commented on HDFS-4300:
-----------------------------------

I think this is okay. A storage failure while downloading will blacklist the storage (I believe
until the SNN is restarted), preventing rename. It also redownloads edits on a future attempt
if the final edits file does not exist. So when we go to rename, we should only be iterating
over valid storages with freshly downloaded files.
                
> TransferFsImage.downloadEditsToStorage should use a tmp file for destination
> ----------------------------------------------------------------------------
>
>                 Key: HDFS-4300
>                 URL: https://issues.apache.org/jira/browse/HDFS-4300
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 2.0.2-alpha
>            Reporter: Todd Lipcon
>            Assignee: Andrew Wang
>            Priority: Critical
>         Attachments: hdfs-4300-1.patch
>
>
> Currently, in TransferFsImage.downloadEditsToStorage, we download the edits file directly
to its finalized path. So, if the transfer fails in the middle, a half-written file is left
and cannot be distinguished from a correct file. So, future checkpoints by the 2NN will fail,
since the file is truncated in the middle -- but it won't ever download a good copy because
it thinks it already has the proper file.

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