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From "Milind Bhandarkar (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-3221) Need a "LineBasedTextInputFormat"
Date Wed, 09 Apr 2008 20:50:08 GMT
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

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,

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"

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