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From "Zheng Shao (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-3341) make key-value separators in hadoop streaming fully configurable
Date Thu, 26 Jun 2008 19:53:45 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-3341?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Zheng Shao updated HADOOP-3341:
-------------------------------

    Attachment: 3341-5.patch

Allow multi-character separators in streaming map/reduce input/output.


> make key-value separators in hadoop streaming fully configurable
> ----------------------------------------------------------------
>
>                 Key: HADOOP-3341
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3341
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: contrib/streaming
>            Reporter: Zheng Shao
>            Assignee: Zheng Shao
>         Attachments: 3341-1.patch, 3341-2.patch, 3341-3.patch, 3341-4.patch, 3341-5.patch
>
>
> By default, hadoop streaming uses TAB as the separator in all places.  However in some
environments, user may want to use customized separators (e.g, ^A = \u0001).
> The separator logic in hadoop streaming is very convoluted. Here is a brief summary:
> InputFormat {
>     KeyValueLineRecordReader.java:59:
> S1: String sepStr = job.get("key.value.separator.in.input.line", "\t");
> }
> Mapper {
>     PipeMapper.java:88: 
> S2: clientOut_.write('\t');
>     Call mapper process
>     PipeMapRed.java:124:
> S3: String mapOutputFieldSeparator = job_.get("stream.map.output.field.separator", "\t");
>     PipeMapRed.java:128:
>     this.numOfMapOutputKeyFields = job_.getInt("stream.num.map.output.key.fields", 1);
> }
> Reducer {
>     PipeReducer.java:78:
> S4: clientOut_.write('\t');
>     Call reducer process
>     PipeMapRed.java:125:
> S5: String reduceOutputFieldSeparator = job_.get("stream.reduce.output.field.separator",
"\t");
>     PipeMapRed.java:129:
>     this.numOfReduceOutputKeyFields = job_.getInt("stream.num.reduce.output.key.fields",
1);
> }
> OutputFormat {
>     TextOuputFormat.java:112:
> S6: String keyValueSeparator = job.get("mapred.textoutputformat.separator", "\t");
> }
> Short-cuts: 
> 1. In case we use "TextInputFormat", S1 and S2 are not used at all. Lines are directly
feed into the mapper (through the value part of the key-value pair - keys, which are offsets,
are directly ignored).
> 2. For jobs with no reducers, The "Reducer" step is skipped.
> We need to make S3 and S4 configurable, possibly under the following names for conformity:
> stream.map.input.field.separator
> stream.reduce.input.field.separator
> Then, by specifying: -jobconf key.value.separator.in.input.line=^A -jobconf stream.map.input.field.separator=^A
-jobconf stream.map.output.field.separator=^A -jobconf stream.reducer.input.field.separator=^A
-jobconf stream.reducer.output.field.separator=^A -jobconf mapred.textoutputformat.separator=^A,
we will be able to use ^A instead of TAB in every place!
> Maybe hadoop streaming can also provide a single option to override these 6 options.

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