[HADOOP-1292] dfs -copyToLocal should guarantee file is complete

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.14.0
• Assignee: Tsz-wo Sze
• Reporter: Eric Baldeschwieler
• Created: 24/Apr/07 17:26
• Updated: 08/Jul/09 16:42
• Resolved: 22/Jun/07 22:48

Description

We should copy to a temporary file, maybe _tmp.<realname>, and then rename the file when the copy is complete. Restarting a copy should reuse the _tmp file, just checksumming it. Then ^Cing a copy will do the right thing.

Original suggestion:

On Apr 23, 2007, at 2:38 AM, Richard Kasperski wrote:

I'd like to have a guarantee that a file copy is both completed and that the file is whole. In the past I've done this by copying the file to a temporary name tmp.<realname> and then moving it to <realname> once I have the file copy is complete. This has the following very nice properties; If the <realname> exists then the file copy is complete and I'm not looking at a partial copy of the file. I believe that the copy to the cluster has both of these properties in that the file doesn't appear in a DFS directory until the whole file has been copied. The copy from the cluster to a local file system does not have these guarantees and it would be very nice if it did. There are two scenarios under what I wish to use this. First is that if I ctrl-c the 'hadoop dfs -copyToLocal' I know what parts are complete and what parts aren't. Second I can run a background compressor to compress the files as they are copied.