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https://issues.apache.org/jira/browse/HADOOP-1986?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12540516
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Doug Cutting commented on HADOOP-1986:
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> X should allow creation of multiple instances of its serializer [ ...]
I don't see how this is required by anything I've proposed. If class names are
serialized with class data, then a single serializer instance could be returned
for a large number of different classes. If class names are not serialized
with class data, then a different serializer instance could be returned for
each class, but these could be cached, so that no more than a single instance
is created per serialized class. If a factory creates multiple instances of
its serializer, and those instances share state, then yes, they are responsible
for coordinating their state. That seems reasonable and expected.
> X needs to be able to both create objects before deserializing them and take
> in a reference to an object and initialize its member variables with
> deserialized data.
No. It must be able to create instances, but it need not use a passed in
reference. As an optimization it may use a reference passed in when optimized
client code passes in non-null references. The implementation and use of
references is optional.
> At this point, I think it's a gut call. If we feel that having clients not
> replicate platform logic is more important than the restrictions we're
> providing on serialization platforms, that's fine.
Yes, I think having clients not replicate platform logic is a mandate. The
framework should maximally encapsulate serialization logic. But I still don't
see what onerous restrictions this inflicts on serialization platforms.
> Add support for a general serialization mechanism for Map Reduce
> ----------------------------------------------------------------
>
> Key: HADOOP-1986
> URL: https://issues.apache.org/jira/browse/HADOOP-1986
> Project: Hadoop
> Issue Type: New Feature
> Components: mapred
> Reporter: Tom White
> Assignee: Tom White
> Fix For: 0.16.0
>
> Attachments: SerializableWritable.java, serializer-v1.patch
>
>
> Currently Map Reduce programs have to use WritableComparable-Writable
> key-value pairs. While it's possible to write Writable wrappers for other
> serialization frameworks (such as Thrift), this is not very convenient: it
> would be nicer to be able to use arbitrary types directly, without explicit
> wrapping and unwrapping.
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