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Posted to mapreduce-issues@hadoop.apache.org by "Hadoop QA (JIRA)" <ji...@apache.org> on 2013/03/14 02:23:11 UTC
[jira] [Commented] (MAPREDUCE-5065) DistCp should skip checksum
comparisons if block-sizes are different on source/target.
[ https://issues.apache.org/jira/browse/MAPREDUCE-5065?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13601937#comment-13601937 ]
Hadoop QA commented on MAPREDUCE-5065:
--------------------------------------
{color:red}-1 overall{color}. Here are the results of testing the latest attachment
http://issues.apache.org/jira/secure/attachment/12573645/MAPREDUCE-5065.branch23.patch
against trunk revision .
{color:red}-1 patch{color}. The patch command could not apply the patch.
Console output: https://builds.apache.org/job/PreCommit-MAPREDUCE-Build/3412//console
This message is automatically generated.
> 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
> Attachments: MAPREDUCE-5065.branch23.patch, MAPREDUCE-5065.branch2.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.
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