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https://issues.apache.org/jira/browse/MAPREDUCE-1183?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12776925#action_12776925
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guillaume viland commented on MAPREDUCE-1183:
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> Allowing applications to store state in the Mapper and/or Reducer will allow
> for more natural semantics and will stop them using DistributedCache for
> trivial state management.
Could you explain and show examples of "applications storing state" ? In a
MapReduce framework what is the meaning of stateless/statefull ?
> Serializable job components: Mapper, Reducer, InputFormat, OutputFormat et al
> -----------------------------------------------------------------------------
>
> Key: MAPREDUCE-1183
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1183
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Components: client
> Affects Versions: 0.21.0
> Reporter: Arun C Murthy
> Assignee: Arun C Murthy
>
> Currently the Map-Reduce framework uses Configuration to pass information
> about the various aspects of a job such as Mapper, Reducer, InputFormat,
> OutputFormat, OutputCommitter etc. and application developers use
> org.apache.hadoop.mapreduce.Job.set*Class apis to set them at job-submission
> time:
> {noformat}
> Job.setMapperClass(IdentityMapper.class);
> Job.setReducerClass(IdentityReducer.class);
> Job.setInputFormatClass(TextInputFormat.class);
> Job.setOutputFormatClass(TextOutputFormat.class);
> ...
> {noformat}
> The proposal is that we move to a model where end-users interact with
> org.apache.hadoop.mapreduce.Job via actual objects which are then serialized
> by the framework:
> {noformat}
> Job.setMapper(new IdentityMapper());
> Job.setReducer(new IdentityReducer());
> Job.setInputFormat(new TextInputFormat("in"));
> Job.setOutputFormat(new TextOutputFormat("out"));
> ...
> {noformat}
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