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https://issues.apache.org/jira/browse/HADOOP-3380?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Enis Soztutar updated HADOOP-3380:
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Attachment: comparator_wip1.patch
bq. I think the fact that the raw comparators depend on the serialization used
is precisely why Doug wants to put it there.
Yes, but my point is that, the *default* comparator returned by some
serialization cannot do much except for deserializing the objects and calling
compareTo on them. Is this assumption not correct? In either case, the
developer has to write its own comparator for a specific class, under a known
serialization.
If we want to allow different raw comparators for different serializations (of
the same class), then we may define the API like :
{code}
RawComparator c = new
SerializationFactory(conf).getSerialization(MyKey.class).getComparator(MyKey.class);
{code}
Note that getComparator() takes the class as an argument so that it can return
a registered comparator for that class, if any, if not it can return the
default(deserializing) comparator.
If we do not want to allow different raw comparators, then wouldn't the
attached (half-baked) patch be enough ?
> 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
> Attachments: comparator_wip1.patch
>
>
> 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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