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https://issues.apache.org/jira/browse/HADOOP-11794?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15936105#comment-15936105
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Steve Loughran commented on HADOOP-11794:
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bq. Is there any reason not to use FileSystem.concat &
FileSystem.getFileBlockLocations ?
{{FileSystem.getFileBlockLocations }} is something filesystems have to
implement this otherwise basic client code fails; if they don't have locality
they tend just to say "localhost" and 1 block.
Concat though, barely implemented. As the [FS spec
says|http://hadoop.apache.org/docs/r3.0.0-alpha2/hadoop-project-dist/hadoop-common/filesystem/filesystem.html#void_concatPath_p_Path_sources],
"This is a little-used operation currently implemented only by HDFS"
Looking for subclasses of FileSyste.concat() It looks like only: hdfs, webhdfs,
httpfs, filterfilesystem do lt.
supporting webhdfs would be really good, as its the one recommended for
cross-hadoop version distcp, and long-haul.
For now, how about have it it check for HDFS and webhdfs and rejects if
anything else.
> distcp can copy blocks in parallel
> ----------------------------------
>
> Key: HADOOP-11794
> URL: https://issues.apache.org/jira/browse/HADOOP-11794
> Project: Hadoop Common
> Issue Type: Improvement
> Components: tools/distcp
> Affects Versions: 0.21.0
> Reporter: dhruba borthakur
> Assignee: Yongjun Zhang
> Attachments: HADOOP-11794.001.patch, HADOOP-11794.002.patch,
> HADOOP-11794.003.patch, HADOOP-11794.004.patch, HADOOP-11794.005.patch,
> HADOOP-11794.006.patch, HADOOP-11794.007.patch, HADOOP-11794.008.patch,
> MAPREDUCE-2257.patch
>
>
> The minimum unit of work for a distcp task is a file. We have files that are
> greater than 1 TB with a block size of 1 GB. If we use distcp to copy these
> files, the tasks either take a long long long time or finally fails. A better
> way for distcp would be to copy all the source blocks in parallel, and then
> stich the blocks back to files at the destination via the HDFS Concat API
> (HDFS-222)
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