Daisuke Kobayashi created HADOOP-16756:
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Summary: Inconsistent Behavior on distcp -update over S3
Key: HADOOP-16756
URL: https://issues.apache.org/jira/browse/HADOOP-16756
Project: Hadoop Common
Issue Type: Bug
Affects Versions: 3.3.0
Reporter: Daisuke Kobayashi
Distcp over S3A always copies all source files no matter the files are changed
or not. This is opposite to the statement in the doc below.
[http://hadoop.apache.org/docs/current/hadoop-distcp/DistCp.html]
{noformat}
And to use -update to only copy changed files.
{noformat}
CopyMapper compares file length as well as block size before copying. While the
file length should match, the block size does not. This is apparently because
the returned block size from S3A is always 32MB.
[https://github.com/apache/hadoop/blob/release-3.2.0-RC1/hadoop-tools/hadoop-distcp/src/main/java/org/apache/hadoop/tools/mapred/CopyMapper.java#L348]
I'd suppose we should update the documentation or make code change.
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