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From "Amareshwari Sriramadasu (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-3221) Need a "LineBasedTextInputFormat"
Date Fri, 09 May 2008 07:24:55 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-3221?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Amareshwari Sriramadasu updated HADOOP-3221:
--------------------------------------------

    Attachment: patch-3221.txt

Here is a patch doing the implementation in the following way:
1. Adds Classes org.apache.hadoop.mapred.LineSplit, org.apache.hadoop.mapred.NLineInputFormat
and
org.apache.hadoop.mapred.NLineInputFormat.NLineRecordReader. Adds a test org.apache.hadoop.mapred.TestLineInputFormat

2. LineSplit implements InputSplit. LineSplit has number of lines and the lines themselves,
sothat all the mappers do not have to fetch the same file simultaneously.

3. NLineInputFormat extends FileInputFormat. It splits the input into N lines per split, where
N is derived from the number of map tasks specified (through mapred.map.tasks in JobConf).
The value of N defaults to 1.

4. NLineRecordReader reads one line at time from the LineSplit. The (key, value) is (LongWritable,
Text), where key is the line number and the value is the line.

Thoughts?

> Need a "LineBasedTextInputFormat"
> ---------------------------------
>
>                 Key: HADOOP-3221
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3221
>             Project: Hadoop Core
>          Issue Type: New Feature
>          Components: mapred
>    Affects Versions: 0.16.2
>         Environment: All
>            Reporter: Milind Bhandarkar
>            Assignee: Amareshwari Sriramadasu
>         Attachments: patch-3221.txt
>
>
> In many "pleasantly" parallel applications, each process/mapper processes the same input
file (s), but with computations are controlled by different parameters.
> (Referred to as "parameter sweeps").
> One way to achieve this, is to specify a set of parameters (one set per line) as input
in a control file (which is the input path to the map-reduce application, where as the input
dataset is specified via a config variable in JobConf.).
> It would be great to have an InputFormat, that splits the input file such that by default,
one line is fed as a value to one map task, and key could be line number. i.e. (k,v) is (LongWritable,
Text).
> If user specifies the number of maps explicitly, each mapper should get a contiguous
chunk of lines (so as to load balance between the mappers.)
> The location hints for the splits should not be derived from the input file, but rather,
should span the whole mapred cluster.
> (Is there a way to do this without having to return an array of nSplits*nTaskTrackers
?)
> Increasing the replication of the "real" input dataset (since it will be fetched by all
the nodes) is orthogonal, and one can use DistributedCache for that.
> (P.S. Please chose a better name for this InputFormat. I am not in love with  "LineBasedText"
name.)

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