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https://issues.apache.org/jira/browse/MAPREDUCE-3992?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13226470#comment-13226470
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Steve Loughran commented on MAPREDUCE-3992:
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@Todd, which class should I look at here?
the content-length header is what should really be set, as that allows the
recipient to recognise another failure mode.
# the output servlet successfully writes all the data
# it calls flush() to flush the buffer to the socket stream.
# the connection goes down through the miracle that is TCP/IP
# the recipient sees the end of the HTTP response, and assumes that the entire
dataset has arrived safely.
# The error propagates.
There are also risks of corruption in the payload that neither the Ether or TCP
protocols pick up on; every layer has a flaw.
See
* Loughran 2011, _did you really want that data_
[Presentation|http://www.slideshare.net/steve_l/did-you-reallywantthatdata]
* Stone & Partridge 2000, _When The CRC and TCP Checksum Disagree_
[Paper|http://www-static.cc.gatech.edu/classes/AY2002/cs8803d_spring/papers/checksum.pdf]
Packet corruption is more likely long-haul than in-datacentre, so I'm not going
to advocate the Content-MD5 overhead, but content-length can only be a good
thing, provide the response length is known in advance (which it never is with
JSP pages, but that's a separate issue)
> Reduce fetcher doesn't verify HTTP status code of response
> ----------------------------------------------------------
>
> Key: MAPREDUCE-3992
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-3992
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: mrv1
> Affects Versions: 1.0.1
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
>
> Currently, the reduce fetch code doesn't check the HTTP status code of the
> response. This can lead to the following situation:
> - the map output servlet gets an IOException after setting the headers but
> before the first call to flush()
> - this causes it to send a response with a non-OK result code, including the
> exception text as the response body (response.sendError() does this if the
> response isn't committed)
> - it will still include the response headers indicating it's a valid response
> In the case of a merge-to-memory, the compression codec might then try to
> interpret the HTML response as compressed data, resulting in either a huge
> allocation (OOME) or some other nasty error. This bug seems to be present in
> MR1, but haven't checked trunk/MR2 yet.
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