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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
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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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