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https://issues.apache.org/jira/browse/HADOOP-11794?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15848116#comment-15848116
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Yongjun Zhang commented on HADOOP-11794:
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Hi [~mithun],
Thanks you so much for the review and all the good comments!
I just uploaded rev 004 to address all of them.
* To answer your question in 3, to avoid the extra RPC call to get all blocks
of a file, I checked the file size first, if so, then get all blocks of the
file, and check if the number of blocks is bigger than {{blocksPerChunk}}. So
it's possible that a file with many small blocks are not split. But I think
that should be ok, because the patch here intend to deal with really large file.
* About 6. the logging is already done in the method {{mergeFileChunks}}, when
debug logging is enabled.
In addition, I also added one more condition to check if the source FS is
DistributedFileSystem, otherwise, the file won't be splitted too.
Wonder if you could take a look at the new patch.
Thanks a lot.
> 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, 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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