[jira] [Commented] (HADOOP-16756) Inconsistent Behavior on distcp -update over S3

["Steve Loughran (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-16756?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17006843#comment-17006843 ] 

Steve Loughran commented on HADOOP-16756:
-----------------------------------------

Reviewing this. turns out that the default attribute to preserve is the block size (OptionsParser L201). And there's no obvious way to turn off

Try doing a distcp with: -direct -pr

this says "preserve replication", which Will be ignored on S3.

If this makes it go away and we need to think about what to do.

One option is for S3A to actually use the block size parameter passed into createFile. We would have to do the same for ABFS too. I wonder what would break.

> Inconsistent Behavior on distcp -update over S3
> -----------------------------------------------
>
>                 Key: HADOOP-16756
>                 URL: https://issues.apache.org/jira/browse/HADOOP-16756
>             Project: Hadoop Common
>          Issue Type: Sub-task
>          Components: fs/s3, tools/distcp
>    Affects Versions: 3.3.0
>            Reporter: Daisuke Kobayashi
>            Priority: Major
>
> 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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