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https://issues.apache.org/jira/browse/HADOOP-1230?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12574002#action_12574002
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Tom White commented on HADOOP-1230:
-----------------------------------
+1
Here are a few comments:
# Closeable is passed a context - is this needed? Also, is it true that not all
methods will work there - e.g. collect?
# We've lost the Iterator interface in Reducers - it would be nice to keep
this, if possible, as it's a standard Java idiom and people expect to be able
to iterate using "foreach".
# If we're creating a new JobConf then it might be a good opportunity to
reconsider its interface if there are things we want to change (not sure if
this is true).
# The formal type parameters have lowercase letters, leading to possible
confusion with types. From the Java Generics Tutorial:
{quote}
We recommend that you use pithy (single character
if possible) yet evocative names for formal type parameters. It's best to
avoid lower
case characters in those names, making it easy to distinguish formal type
parameters
from ordinary classes and interfaces.
{quote}
I prefer K1, V1, K2, V2, K3, V3 when emphasizing the relation between all
types in a MapReduce job, or K, V when this distinction is not important. Other
possibilities would be KI, VI, KO, VO, or KIN, VIN, KOUT, VOUT.
> Replace parameters with context objects in Mapper, Reducer, Partitioner,
> InputFormat, and OutputFormat classes
> --------------------------------------------------------------------------------------------------------------
>
> Key: HADOOP-1230
> URL: https://issues.apache.org/jira/browse/HADOOP-1230
> Project: Hadoop Core
> Issue Type: Improvement
> Components: mapred
> Reporter: Owen O'Malley
> Assignee: Owen O'Malley
> Attachments: context-objs.patch
>
>
> This is a big change, but it will future-proof our API's. To maintain
> backwards compatibility, I'd suggest that we move over to a new package name
> (org.apache.hadoop.mapreduce) and deprecate the old interfaces and package.
> Basically, it will replace:
> package org.apache.hadoop.mapred;
> public interface Mapper extends JobConfigurable, Closeable {
> void map(WritableComparable key, Writable value, OutputCollector output,
> Reporter reporter) throws IOException;
> }
> with:
> package org.apache.hadoop.mapreduce;
> public interface Mapper extends Closable {
> void map(MapContext context) throws IOException;
> }
> where MapContext has the methods like getKey(), getValue(), collect(Key,
> Value), progress(), etc.
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