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https://issues.apache.org/jira/browse/HADOOP-3941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12625847#action_12625847
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Tsz Wo (Nicholas), SZE commented on HADOOP-3941:
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> ... so returning null seems a better choice than an exception here. Another
> option might be to return a trivial checksum, e.g., the file's length.
I think returning null make sense. We cannot return a trivial checksum since
an algorithm is specified in the call. We should only return the checksum
generated by the specified algorithm.
> Should we extend distcp to use this?
Yes, the canonical application is distcp. I could also change distcp to use
the new API.
> Extend FileSystem API to return file-checksums/file-digests
> -----------------------------------------------------------
>
> Key: HADOOP-3941
> URL: https://issues.apache.org/jira/browse/HADOOP-3941
> Project: Hadoop Core
> Issue Type: New Feature
> Components: fs
> Reporter: Tsz Wo (Nicholas), SZE
> Attachments: 3941_20080818.patch, 3941_20080819.patch,
> 3941_20080819b.patch, 3941_20080820.patch
>
>
> Suppose we have two files in two locations (may be two clusters) and these
> two files have the same size. How could we tell whether the content of them
> are the same?
> Currently, the only way is to read both files and compare the content of
> them. This is a very expensive operation if the files are huge.
> So, we would like to extend the FileSystem API to support returning
> file-checksums/file-digests.
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