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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-3574) Fix small race and do some cleanup in GetImageServlet
Date Tue, 03 Jul 2012 20:56:35 GMT

     [ https://issues.apache.org/jira/browse/HDFS-3574?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Todd Lipcon updated HDFS-3574:
------------------------------

       Resolution: Fixed
    Fix Version/s: 2.0.1-alpha
     Hadoop Flags: Reviewed
           Status: Resolved  (was: Patch Available)

Committed to branch-2 and trunk, thanks Aaron.
                
> Fix small race and do some cleanup in GetImageServlet
> -----------------------------------------------------
>
>                 Key: HDFS-3574
>                 URL: https://issues.apache.org/jira/browse/HDFS-3574
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: name-node
>    Affects Versions: 3.0.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Minor
>             Fix For: 2.0.1-alpha
>
>         Attachments: hdfs-3574.txt, hdfs-3574.txt, hdfs-3574.txt, hdfs-3574.txt
>
>
> There's a very small race window in GetImageServlet, if the following interleaving occurs:
> - The Storage object returns some local file in the storage directory (eg an edits file
or image file)
> - *Race*: some other process removes the file
> - GetImageServlet calls file.length() which returns 0, since it doesn't exist. It thus
faithfully sets the Content-Length header to 0
> - getFileClient() throws FileNotFoundException when trying to open the file. But, since
we call response.getOutputStream() before this, the headers have already been sent, so we
fail to send the "404" or "500" response that we should.
> Thus, the client sees a 0-length Content-Length followed by 0 lengths of content, and
thinks it successfully has downloaded the target file, where in fact it downloads an empty
one.
> I saw this in practice during the "edits synchronization" phase of recovery while working
on HDFS-3077, though it could apply on existing code paths, as well, I believe.

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