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Date: Tue, 9 Oct 2007 23:22:50 -0700 (PDT)
From: "Vivek Ratan (JIRA)" <jira@apache.org>
To: hadoop-dev@lucene.apache.org
Subject: [jira] Commented: (HADOOP-1986) Add support for a general
 serialization mechanism for Map Reduce
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    [ https://issues.apache.org/jira/browse/HADOOP-1986?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12533622 ] 

Vivek Ratan commented on HADOOP-1986:
-------------------------------------

I forgot to add - using introspection to walk through a class has some more problems. Things like versioning, and other kinds of optimizations will be difficult with general introspection. As someone mentioned in the Thrift discussion, it also doesn't handle field IDs in DDLs, and other features (such as default values, optional fields) that serialization platforms  will want to support. For such cases, DDL-generated classes are better. By offering both approaches, we can let users and developers decide on the tradeoff : ease of use versus more complicated functionality. 

> 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
>
>
> 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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