[jira] Commented: (HADOOP-3914) checksumOk implementation in DFSClient can break applications

["Hadoop QA (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-3914?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12640679#action_12640679 ] 

Hadoop QA commented on HADOOP-3914:
-----------------------------------

-1 overall.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12390147/patch.HADOOP-3914
  against trunk revision 705691.

    +1 @author.  The patch does not contain any @author tags.

    -1 tests included.  The patch doesn't appear to include any new or modified tests.
                        Please justify why no tests are needed for this patch.

    +1 javadoc.  The javadoc tool did not generate any warning messages.

    +1 javac.  The applied patch does not increase the total number of javac compiler warnings.

    +1 findbugs.  The patch does not introduce any new Findbugs warnings.

    +1 Eclipse classpath. The patch retains Eclipse classpath integrity.

    +1 core tests.  The patch passed core unit tests.

    +1 contrib tests.  The patch passed contrib unit tests.

Test results: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/3487/testReport/
Findbugs warnings: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/3487/artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Checkstyle results: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/3487/artifact/trunk/build/test/checkstyle-errors.html
Console output: http://hudson.zones.apache.org/hudson/job/Hadoop-Patch/3487/console

This message is automatically generated.

> checksumOk implementation in DFSClient can break applications
> -------------------------------------------------------------
>
>                 Key: HADOOP-3914
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3914
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.17.1
>            Reporter: Christian Kunz
>            Assignee: Christian Kunz
>             Fix For: 0.19.0
>
>         Attachments: patch.HADOOP-3914
>
>
> One of our non-map-reduce applications (written in C and using libhdfs to access dfs) stopped working after switch from 0.16 to 0.17.
> The problem was finally traced down to failures in checksumOk.
> I would assume, the purpose of checksumOk is for a DfsClient to indicate to a sending Datanode that the checksum of the received block is okay. This must be useful in the replication pipeline.
> How checksumOk is implemented is that any IOException is caught and ignored, probably because it is not essential for the client that the message is successful.
> But it proved fatal for our application because this application links in a 3rd-party library which seems to catch socket exceptions before libhdfs.
> Why was there an Exception? In our case the application reads a file into the local buffer of the DFSInputStream large enough to hold all data, the application reads to the end  and the checksumOK is sent successfully at that time. But then the application does some other stuff and comes back to re-read the file (still open). It is then when it calls checksumOk again and crashes.
> It can easily be avoided by adding a Boolean making sure that checksumOk is called exactly once when EOS is encountered. Redundant calls to checksumOk do not seem to make sense anyhow.

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