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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3981) Need a distributed file checksum algorithm for HDFS
Date Wed, 10 Sep 2008 16:25:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3981?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12629854#action_12629854
] 

Doug Cutting commented on HADOOP-3981:
--------------------------------------

Some comments:
 - It looks like you forgot to include the class MD5MD5CRC32FileChecksum in the patch.
 - Why do you use the datanode's socket/opcode interface rather than adding a method to ClientDatanodeProtocol?
 - WritableUtils#toByteArray can use io.DataOutputBuffer, no?
 - DistCp#sameFile() should be changed to only get checksums when the lengths differ.



> Need a distributed file checksum algorithm for HDFS
> ---------------------------------------------------
>
>                 Key: HADOOP-3981
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3981
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: dfs
>            Reporter: Tsz Wo (Nicholas), SZE
>         Attachments: 3981_20080909.patch
>
>
> Traditional message digest algorithms, like MD5, SHA1, etc., require reading the entire
input message sequentially in a central location.  HDFS supports large files with multiple
tera bytes.  The overhead of reading the entire file is huge. A distributed file checksum
algorithm is needed for HDFS.

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