[HADOOP-14137] Faster distcp by taking file list from fsimage or -lsr result

• Type: New Feature
• Status: Patch Available
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.6.5
• Fix Version/s: 2.6.6
• Component/s: tools/distcp
• Assignee: Zheng Shao
• Reporter: Zheng Shao
• Created: 02/Mar/17 02:52
• Updated: 14/Mar/17 11:34

Description

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 "-listing <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.