[jira] Commented: (HADOOP-3941) Extend FileSystem API to return file-checksums/file-digests

["Doug Cutting (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-3941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12628457#action_12628457 ] 

Doug Cutting commented on HADOOP-3941:
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> We might need a method for getting the supported algorithms of a file system.

If we remove the "algorithm" parameter to getFileChecksum() then each FileSystem would simply return checksums using its native algorithm.  When these match, cross-filesystem copies would be checksummed.  Later, if we have filesystems that implement multiple checksum algorithms, we might consider something more elaborate, but that seems sufficient for now, no?


> 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
>            Assignee: Tsz Wo (Nicholas), SZE
>         Attachments: 3941_20080818.patch, 3941_20080819.patch, 3941_20080819b.patch, 3941_20080820.patch, 3941_20080826.patch, 3941_20080827.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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