[jira] Commented: (HADOOP-3149) supporting multiple outputs for M/R jobs

["Hudson (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-3149?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12624664#action_12624664 ] 

Hudson commented on HADOOP-3149:
--------------------------------

Integrated in Hadoop-trunk #581 (See [http://hudson.zones.apache.org/hudson/job/Hadoop-trunk/581/])

> supporting multiple outputs for M/R jobs
> ----------------------------------------
>
>                 Key: HADOOP-3149
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3149
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: mapred
>         Environment: all
>            Reporter: Alejandro Abdelnur
>            Assignee: Alejandro Abdelnur
>             Fix For: 0.19.0
>
>         Attachments: patch3149.txt, patch3149.txt, patch3149.txt, patch3149.txt, patch3149.txt, patch3149.txt, patch3149.txt, patch3149.txt, patch3149.txt, patch3149.txt, patch3149.txt, patch3149.txt, patch3149.txt, patch3149.txt, patch3149.txt, patch3149.txt
>
>
> The outputcollector supports writing data to a single output, the 'part' files in the output path.
> We found quite common that our M/R jobs have to write data to different output. For example when classifying data as NEW, UPDATE, DELETE, NO-CHANGE to later do different processing on it.
> Handling the initialization of additional outputs from within the M/R code complicates the code and is counter intuitive with the notion of job configuration.
> It would be desirable to:
> # Configure the additional outputs in the jobconf, potentially specifying different outputformats, key and value classes for each one.
> # Write to the additional outputs in a similar way as data is written to the outputcollector.
> # Support the speculative execution semantics for the output files, only visible in the final output for promoted tasks.
> To support multiple outputs the following classes would be added to mapred/lib:
> * {{MOJobConf}} : extends {{JobConf}} adding methods to define named outputs (name, outputformat, key class, value class)
> * {{MOOutputCollector}} : extends {{OutputCollector}} adding a {{collect(String outputName, WritableComparable key, Writable value)}} method.
> * {{MOMapper}} and {{MOReducer}}: implement {{Mapper}} and {{Reducer}} adding a new {{configure}}, {{map}} and {{reduce}} signature that take the corresponding {{MO}} classes and performs the proper initialization.
> The data flow behavior would be: key/values written to the default (unnamed) output (using the original OutputCollector {{collect}} signature) take part of the shuffle/sort/reduce processing phases. key/values written to a named output from within a map don't.
> The named output files would be named using the task type and task ID to avoid collision among tasks (i.e. 'new-m-00002' and 'new-r-00001').
> Together with the setInputPathFilter feature introduced by HADOOP-2055 it would become very easy to chain jobs working on particular named outputs within a single directory.
> We are using heavily this pattern and it greatly simplified our M/R code as well as chaining different M/R. 
> We wanted to contribute this back to Hadoop as we think is a generic feature many could benefit from.

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