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https://issues.apache.org/jira/browse/HADOOP-8065?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15273160#comment-15273160
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Ravi Prakash commented on HADOOP-8065:
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Thanks Suraj!
In CopyMapper, you are declaring {{codec}}, assigning it a value and then never
using it. Are you sure you need those changes? Maybe you are missing some part
of the patch? I am looking at
[HADOOP-8065-trunk_2016-04-29-4.patch|https://issues.apache.org/jira/secure/attachment/12801507/HADOOP-8065-trunk_2016-04-29-4.patch]
To enable compression during transit is a MUCH bigger Epic. We may have to
change
[FileSystem|https://github.com/apache/hadoop/blob/trunk/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FileSystem.java#L769],
and
[BlockSender|https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BlockSender.java]
amongst others (on the datanode side). A lot more people will also have an
opinion on it and its probably a multi-month effort. Also, striped blocks may
make it more complicated. People may argue that users should compress and
decompress at the application level. It'd just be way more complicated than
what we are trying to do here. I suggest we tackle that after this problem
> distcp should have an option to compress data while copying.
> ------------------------------------------------------------
>
> Key: HADOOP-8065
> URL: https://issues.apache.org/jira/browse/HADOOP-8065
> Project: Hadoop Common
> Issue Type: Improvement
> Components: fs
> Affects Versions: 0.20.2
> Reporter: Suresh Antony
> Assignee: Suraj Nayak
> Priority: Minor
> Labels: distcp
> Fix For: 0.20.2
>
> Attachments: HADOOP-8065-trunk_2015-11-03.patch,
> HADOOP-8065-trunk_2015-11-04.patch, HADOOP-8065-trunk_2016-04-29-4.patch,
> patch.distcp.2012-02-10
>
>
> We would like compress the data while transferring from our source system to
> target system. One way to do this is to write a map/reduce job to compress
> that after/before being transferred. This looks inefficient.
> Since distcp already reading writing data it would be better if it can
> accomplish while doing this.
> Flip side of this is that distcp -update option can not check file size
> before copying data. It can only check for the existence of file.
> So I propose if -compress option is given then file size is not checked.
> Also when we copy file appropriate extension needs to be added to file
> depending on compression type.
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