Need a "LineBasedTextInputFormat"
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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, 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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