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https://issues.apache.org/jira/browse/HADOOP-14137?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15892582#comment-15892582
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Erik Krogen commented on HADOOP-14137:
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+1 on this, we have just recently made similar efforts when trying to do a
DistCp of very large numbers of files and I think it is useful in general. One
note, you'll also have to provide a way for the user to specify what directory
the files should be considered relative to (e.g. if one of the listed files is
"/user/erik/dir/file", how much of that directory structure ends up being
replicated on the target).
Also agreed with Steve that {{--listingFile}} is better than {{-list}}.
> Faster distcp by taking file list from fsimage or -lsr result
> -------------------------------------------------------------
>
> Key: HADOOP-14137
> URL: https://issues.apache.org/jira/browse/HADOOP-14137
> Project: Hadoop Common
> Issue Type: New Feature
> Components: tools/distcp
> Reporter: Zheng Shao
>
> DistCp is very slow to start when the src directory has a huge number of
> subdirectories. In our case, we already have the directory listing (via
> "hdfs oiv -i fsimage" or via nightly "hdfs dfs -lr -r /" dumps), and we would
> like to use that instead of doing realtime listing on the NameNode.
> The "-f" option doesn't help in this case because it would try to put
> everything into a single flat target directory.
> We'd like to introduce a new option "-list <file>" for distcp. The <file>
> contains the result of listing the src directory.
> In order to achieve this, we plan to:
> 1. Add a new CopyListing class PregeneratedCopyListing similar to
> SimpleCopyListing which doesn't "-ls -r" into the directory, but takes the
> listing via "-list"
> 2. Add an option "-list <file>" which will automatically make distcp use the
> new PregeneratedCopyListing class.
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