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From "Aaron T. Myers (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3574) Fix small race and do some cleanup in GetImageServlet
Date Fri, 29 Jun 2012 18:17:45 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3574?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13404085#comment-13404085

Aaron T. Myers commented on HDFS-3574:

The patch looks pretty good to me. One small comment. +1 once this is addressed:

# "throw new FileNotFoundException();" - would be nice to say which file, in two places.
> 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
>         Attachments: 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
> 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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