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https://issues.apache.org/jira/browse/HADOOP-11794?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15937609#comment-15937609
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Chris Douglas commented on HADOOP-11794:
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bq. the current patch would split a file and copy them into chunk files at
target, then at commit stage we will find concat doesn't work, thus the target
is polluted (inconsistent state)
Doesn't this imply that FileSystems that support concat can also be left in an
inconsistent state? If the concat operation fails, the job is
killed/fails/dies, etc. then distcp cleanup should remove partial work. If a
FileSystem doesn't support concat, shouldn't that failure follow the same path?
Either way, +1 on the approach you outline. Thanks for considering the feedback
and updating the patch, [~yzhangal]. Looking forward to this enhancement; it's
been a long time coming!
> 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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