Steve Loughran created HADOOP-15281:
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Summary: Distcp to add no-rename copy option
Key: HADOOP-15281
URL: https://issues.apache.org/jira/browse/HADOOP-15281
Project: Hadoop Common
Issue Type: Improvement
Components: tools/distcp
Affects Versions: 3.0.0
Reporter: Steve Loughran
Assignee: Steve Loughran
Currently Distcp uploads a file by two strategies
# append parts
# copy to temp then rename
option 2 executes the following swquence in {{promoteTmpToTarget}}
{code}
if ((fs.exists(target) && !fs.delete(target, false))
|| (!fs.exists(target.getParent()) && !fs.mkdirs(target.getParent()))
|| !fs.rename(tmpTarget, target)) {
throw new IOException("Failed to promote tmp-file:" + tmpTarget
+ " to: " + target);
}
{code}
For any object store, that's a lot of HTTP requests; for S3A you are looking at
12+ requests and an O(data) copy call.
This is not a good upload strategy for any store which manifests its output
atomically at the end of the write().
Proposed: add a switch to write direct to the dest path. either a conf option
or a CLI option
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