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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-6685) Change the generic serialization framework API to use serialization-specific bytes instead of Map<String,String> for configuration
Date Fri, 19 Nov 2010 00:33:18 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-6685?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12933627#action_12933627
] 

Doug Cutting commented on HADOOP-6685:
--------------------------------------

Eli, thanks for refocusing discussion on the original objective of this issue.  We've gotten
distracted by other aspects not essential to that, and I don't think that primary objective
has ever been agreed on.

I do not agree that an array of bytes is a better way to represent serialization metadata.
 (I stated this in the first comment on this issue.)  I prefer the solutions that were in
HADOOP-6165 and HADOOP-6420.  My objections are:
 - inheritance is used in serialization implementations, and inheritance is harder to implement
with binary objects
 - binary encodings are less transparent and create binary serialization bootstrap problems
 - serialization metadata is not large nor read/written in inner loops, so binary is not required
 - using a binary encoding for serialization metadata will require substantial changes to
serialization clients.  The Map<String,String> approach is easily embedded in existing
metadata, like configurations, jobs, sequencefile, etc., a binary encoding requires changes
to all serialization clients, with little to compensate.  changes to public apis and persistent
data formats should be made only when there is clear end-user value, which i don't see that
a change from Map<String,String> to byte[] provides.

I also will re-voice my objection that the current patch makes a large number of changes beyond
changing the format of serialization metadata.  We should restrict the patch to the description,
and change other things in other issues.

> Change the generic serialization framework API to use serialization-specific bytes instead
of Map<String,String> for configuration
> ----------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-6685
>                 URL: https://issues.apache.org/jira/browse/HADOOP-6685
>             Project: Hadoop Common
>          Issue Type: Improvement
>            Reporter: Owen O'Malley
>            Assignee: Owen O'Malley
>             Fix For: 0.22.0
>
>         Attachments: libthrift.jar, serial.patch, serial4.patch, serial6.patch, SerializationAtSummit.pdf
>
>
> Currently, the generic serialization framework uses Map<String,String> for the
serialization specific configuration. Since this data is really internal to the specific serialization,
I think we should change it to be an opaque binary blob. This will simplify the interface
for defining specific serializations for different contexts (MAPREDUCE-1462). It will also
move us toward having serialized objects for Mappers, Reducers, etc (MAPREDUCE-1183).

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