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Date: Wed, 14 May 2008 23:59:55 -0700 (PDT)
From: "Amareshwari Sriramadasu (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Issue Comment Edited: (HADOOP-3221) Need a
 "LineBasedTextInputFormat"
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    [ https://issues.apache.org/jira/browse/HADOOP-3221?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12597018#action_12597018 ] 

amareshwari edited comment on HADOOP-3221 at 5/14/08 11:58 PM:
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Here is patch adding org.apache.hadoop.mapred.lib.NLineInputFormat, which splits N lines of input file as one split. 
N is specifed using config  variable "mapred.line.input.format.linespermap", defaults to 1.  In files with a number of lines not evenly divided by N, the last split constructed from that file would have number lines lines less than N.

NLineInputFormat constructs FileSplits containing N lines in each split. And Uses LineRecordReader to read the lines from the split.

      was (Author: amareshwari):
    Here is patch adding org.apache.hadoop.mapred.lib.NLineInputFormat, which splits N lines of input file as one split. 
N is specifed using config  variable "mapred.line.input.format.linespermap", defaults to 1.  In files with a number of lines not evenly divided by N, the last split constructed from that file would have number lines lines less than N.

NLineInputFormat constructs FileSplits containing N lines in each map. And Uses LineRecordReader to read the lines from the split.
  
> 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
>             Fix For: 0.18.0
>
>         Attachments: patch-3221-1.txt, patch-3221-2.txt, 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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