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From "Ranadip (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-2120) dfs -getMerge does not do what it says it does
Date Tue, 20 Sep 2011 21:14:08 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2120?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13109001#comment-13109001
] 

Ranadip commented on HADOOP-2120:
---------------------------------

> hadoop fs -get dir/* - > out

> has the same behavior, no ?

Not exactly same I think. In this case, out is a file on the local filesystem while -getmerge
is supposed to create the merged file on the hdfs.
Of course we can still achieve that doing something like

hadoop fs -get dir/* - | hadoop fs -put - dir/dest

> dfs -getMerge does not do what it says it does
> ----------------------------------------------
>
>                 Key: HADOOP-2120
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2120
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: documentation, fs
>    Affects Versions: 0.14.3
>         Environment: All
>            Reporter: Milind Bhandarkar
>              Labels: newbie
>
> dfs -getMerge, which calls FileUtil.CopyMerge, contains this javadoc:
> {code}
> Get all the files in the directories that match the source file pattern
>    * and merge and sort them to only one file on local fs 
>    * srcf is kept.
> {code}
> However, it only concatenates the set of input files, rather than merging them in sorted
order.
> Ideally, the copyMerge should be equivalent to a map-reduce job with IdentityMapper and
IdentityReducer with numReducers = 1. However, not having to run this as a map-reduce job
has some advantages, since it increases cluster utilization during reduce phase.

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