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https://issues.apache.org/jira/browse/HADOOP-3981?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12629322#action_12629322
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Doug Cutting commented on HADOOP-3981:
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> implement MD5-of-CRC32-every-512bytes-with-64Mblocks and use it as the
> default file checksum algorithm for all FileSystem?
We should just implement this for HDFS, where CRCs already exist.
> Should we return a list of MD5 [ ... ] ?
No, just a single checksum for the entire file.
> If bytes.per.checksum is not 512 or block size is not 64MB in HDFS, how about
> getFileChecksum(Path f) returns null?
No, it should return a different algorithm string, with the file's
bytes.per.checksum and block size. I now think returning null by default is
probably best, rather than having a default implementation that uses file
length, since we should check file lengths explicitly and only compare
checksums when lengths differ.
> For other FS, how about we return null?
Yes, I agree.
> 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
>
> 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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