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lohit vijayarenu commented on HADOOP-3221:
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bq. 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.
+1 on this approach
> 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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