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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3941) Extend FileSystem API to return file-checksums/file-digests
Date Thu, 04 Sep 2008 21:25:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12628464#action_12628464
] 

Tsz Wo (Nicholas), SZE commented on HADOOP-3941:
------------------------------------------------

bq. 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?

+1  Then, I will only add
{code}
public FileChecksum getFileChecksum(Path f) throws IOException
{code}
in this patch.  If we need more checksum algorithms later, we should add these two methods:
{code}
public FileChecksum getFileChecksum(String algorithm, Path f) throws IOException

public String[] getSupportedChecksumAlgorithms()
{code}

> 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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