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https://issues.apache.org/jira/browse/MAPREDUCE-5065?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13633999#comment-13633999
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Hudson commented on MAPREDUCE-5065:
-----------------------------------
Integrated in Hadoop-Hdfs-trunk #1375 (See
[https://builds.apache.org/job/Hadoop-Hdfs-trunk/1375/])
MAPREDUCE-5065. DistCp should skip checksum comparisons if block-sizes are
different on source/target. Contributed by Mithun Radhakrishnan. (Revision
1468629)
Result = FAILURE
kihwal : http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1468629
Files :
* /hadoop/common/trunk/hadoop-mapreduce-project/CHANGES.txt
*
/hadoop/common/trunk/hadoop-tools/hadoop-distcp/src/main/java/org/apache/hadoop/tools/mapred/RetriableFileCopyCommand.java
*
/hadoop/common/trunk/hadoop-tools/hadoop-distcp/src/test/java/org/apache/hadoop/tools/mapred/TestCopyMapper.java
> DistCp should skip checksum comparisons if block-sizes are different on
> source/target.
> --------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-5065
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-5065
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: distcp
> Affects Versions: 2.0.3-alpha, 0.23.5
> Reporter: Mithun Radhakrishnan
> Assignee: Mithun Radhakrishnan
> Fix For: 3.0.0, 2.0.5-beta, 0.23.8
>
> Attachments: MAPREDUCE-5065.branch-0.23.patch,
> MAPREDUCE-5065.branch-2.patch
>
>
> When copying files between 2 clusters with different default block-sizes, one
> sees that the copy fails with a checksum-mismatch, even though the files have
> identical contents.
> The reason is that on HDFS, a file's checksum is unfortunately a function of
> the block-size of the file. So you could have 2 different files with
> identical contents (but different block-sizes) have different checksums.
> (Thus, it's also possible for DistCp to fail to copy files on the same
> file-system, if the source-file's block-size differs from HDFS default, and
> -pb isn't used.)
> I propose that we skip checksum comparisons under the following conditions:
> 1. -skipCrc is specified.
> 2. File-size is 0 (in which case the call to the checksum-servlet is moot).
> 3. source.getBlockSize() != target.getBlockSize(), since the checksums are
> guaranteed to differ in this case.
> I have a patch for #3.
> Edit: I've modified the fix to warn the user (instead of skipping the
> checksum-check). Skipping parity-checks is unsafe. The code now fails the
> copy, and suggests that the user either use -pb to preserve block-size, or
> consider -skipCrc (and forgo copy validation entirely).
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