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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-3981) Need a distributed file checksum algorithm for HDFS
Date Wed, 10 Sep 2008 20:41:44 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-3981?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Tsz Wo (Nicholas), SZE updated HADOOP-3981:
-------------------------------------------

    Attachment: 3981_20080910.patch

3981_20080910.patch: 

> It looks like you forgot to include the class MD5MD5CRC32FileChecksum in the patch.
added MD5MD5CRC32FileChecksum

> Why do you use the datanode's socket/opcode interface rather than adding a method to
ClientDatanodeProtocol?
There might be a RPC timeout problem.  So I use data transfer protocol instead of ClientDatanodeProtocol.

> WritableUtils#toByteArray can use io.DataOutputBuffer, no?
Moved WritableUtils#toByteArray to io.DataOutputBuffer and implemented it with DataOutputBuffer.

> DistCp#sameFile() should be changed to only get checksums when the lengths differ.
Updated DistCp

> 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, 3981_20080910.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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