[jira] [Resolved] (HADOOP-4243) Serialization framework use SequenceFile/TFile/Other metadata to instantiate deserializer

["Allen Wittenauer (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HADOOP-4243?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Allen Wittenauer resolved HADOOP-4243.
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    Resolution: Duplicate

> Serialization framework use SequenceFile/TFile/Other metadata to instantiate deserializer
> -----------------------------------------------------------------------------------------
>
>                 Key: HADOOP-4243
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4243
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: contrib/serialization
>            Reporter: Pete Wyckoff
>
> SequenceFile metadata is useful for storing additional information about the serialized data, for example, for RecordIO, whether the data is CSV or Binary.  For thrift, the same thing - Binary, JSON, ...
> For Hive, this may be especially important, because it has a Dynamic generic serializer/deserializer that takes its DDL at runtime (as opposed to RecordIO and Thrift which require pre-compilation into a specific class whose name can be stored in the sequence file key or value class).   In this case, the class name is like Record.java in RecordIO - it doesn't tell you anything without the DDL.
> One way to address this could be adding the sequence file metadata to the getDeserializer call in Serialization interface.  The api would then be something like getDeserializer(Class<?>, Map<Text, Text> metadata) or Properties metadata.
> But, I am open to proposals.
> This also means that saying a class implements Writable is not enough to necessarily deserialize it since it may do specific actions based on the metadata - e.g., RecordIO might determine whether to use CSV rather than the default Binary deserialization.
> There's the other issue of the getSerializer returning the metadata to be written to the Sequence/T File.



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