[jira] Resolved: (HADOOP-4192) Class Deserializer.getRealClass() method to return the actual class of the objects from a deserializer

["Pete Wyckoff (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HADOOP-4192?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Pete Wyckoff resolved HADOOP-4192.
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    Resolution: Invalid

should be attacking this the other way around by having a way of getting serialization context info - the serialization class and the class to be deserialized and pass these down.


> Class <? extends T> Deserializer.getRealClass() method to return the actual class of the objects from a deserializer
> --------------------------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-4192
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4192
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: mapred
>            Reporter: Pete Wyckoff
>
> Note: this use case is completely for non-self describing files with Serialization framework records.  If the Serialization Class and the actual type of records to be deserialized is configured higher up through the JobConf.  
> It is motivated by the need to create a generic FlatFileDeserializerRecordReader that can be configued to use any Serialization implementation through the JobConf.
> Since A deserializer can return a subtype of the type it is instantiated to return, we can create generic Deserializers for a base type - e.g., Writable, Record, Thrift.Tbase where the RecordReader need not be specific to any of them.  
> In which case,to implement RecordReader.getValueClass();, the generic RecordReader really needs to query that from the Deserializer.
> And since this RecordReader is generic even ithe Serialization Implementation it is going to use should come from the JobConf as should the actual specific class being Deserialized. e.g., Record/MyUserIDRecord, Writable/LongWritable.
> The RecordReader would need to know how the Serialization and Deserializer get their configuration info to implement getValueClass().
> A much cleaner way is to implement getRealClass I think.
>  

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