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