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From "Milind Bhandarkar (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-5979) Streaming partitioner should allow command, not just Java class
Date Tue, 09 Jun 2009 20:17:07 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-5979?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12717809#action_12717809
] 

Milind Bhandarkar commented on HADOOP-5979:
-------------------------------------------

It would be valuable to have a non-java streaming partitioner. It should be executed once
per map task, and should take as input (through stdin), the text-encoded key value pairs (one
per line, separated by field separator), and output on stdout a number (again, text-encoded)
for each key value pair.

Number of partitions, i.e. number of reducers should already be available to this streaming
partitioner as the environment variable mapred_reduce_tasks. So, no need to pass it in each
line.

Partitioner need not be an "advanced" feature. Think about a parallel bucketing operation,
where number of buckets is predetermined, so the mapper makes a decision where each value
should go. In this case, the key is a partition ID, and value is the record to be bucketed.
HashBased partitioner of course does not work in this case. But a streaming partitioner, such
as 'cut -f1' is what is needed.

> Streaming partitioner should allow command, not just Java class
> ---------------------------------------------------------------
>
>                 Key: HADOOP-5979
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5979
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: contrib/streaming
>            Reporter: Klaas Bosteels
>
> Since HADOOP-4842 got committed, Streaming allows both commands and Java classes to be
specified as mapper, reducer, and combiner, but the {{-partitioner}} option is still limited
to Java classes only. Allowing commands to be specified as partitioner as well would greatly
improve the flexibility of Streaming programs.

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