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https://issues.apache.org/jira/browse/HADOOP-3380?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12596484#action_12596484
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Doug Cutting commented on HADOOP-3380:
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> What's the relationship between this proposal and
> JobConf#getOutputValueGroupingComparator() and
> JobConf#getOutputKeyComparator()?
Those are ways to override the "natural" (or default) comparator under
MapReduce. This proposal is about defining the natural comparator. If we had
a good configurable comparator, then we perhaps wouldn't need those methods,
but I'm not sure... The framework might set io.comparator.context=grouping,
and then the configurable comparator implementation could use this to decide to
use the user-specified value of io.record.compare.grouping or somesuch. Yuck!
BTW, those methods should both be altered to return RawComparator, not a
WritableComparator, no?
> need comparators in serializer framework
> ----------------------------------------
>
> Key: HADOOP-3380
> URL: https://issues.apache.org/jira/browse/HADOOP-3380
> Project: Hadoop Core
> Issue Type: New Feature
> Components: io
> Reporter: Doug Cutting
>
> The new serialization framework permits Hadoop to incorporate different
> serialization systems, including Hadoop's Writable, Thrift, Java
> Serialization, etc. It provides a generic, extensible means
> (SerializationFactory) to create serializers and deserializers for arbitrary
> Java classes. However it does not include a generic means to create
> comparators for these classes. Comparators are required for MapReduce keys
> and many other computations. Thus we should enhance the serialization
> framwork to provide comparators too.
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