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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-941) Make Hadoop Record I/O Easier to use outside Hadoop
Date Sat, 24 Feb 2007 01:34:05 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12475568
] 

Doug Cutting commented on HADOOP-941:
-------------------------------------

> The difficulty is precisely in including interfaces from another package.

What's so hard about that?

> It causes generated code to depend on Hadoop.

This is Hadoop, isn't it?

> If we don't want the compiler option, the alternatives are to stop generating the Writable
and WritableComparable interfaces altogether or to make them part of org.apache.hadoop.record

Either of those would be preferable to the current situation, but my first choice is still
simply to include Writable and WritableComparable in any record jar file and be done with
it.  This is not a hard problem.  We've already wasted way too much discussion on it.  We're
solving a non-problem by adding complexity.

> Make Hadoop Record I/O Easier to use outside Hadoop
> ---------------------------------------------------
>
>                 Key: HADOOP-941
>                 URL: https://issues.apache.org/jira/browse/HADOOP-941
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: record
>    Affects Versions: 0.10.1
>         Environment: All
>            Reporter: Milind Bhandarkar
>         Assigned To: Milind Bhandarkar
>         Attachments: jute-patch.txt
>
>
> Hadoop record I/O can be used effectively outside of Hadoop. It would increase its utility
if developers can use it without having to import hadoop classes, or having to depend on Hadoop
jars. Following changes to the current translator and runtime are proposed.
> Proposed Changes:
> 1. Use java.lang.String as a native type for ustring (instead of Text.)
> 2. Provide a Buffer class as a native Java type for buffer (instead of BytesWritable),
so that later BytesWritable could be implemented as following DDL:
> module org.apache.hadoop.io {
>   record BytesWritable {
>     buffer value;
>   }
> }
> 3. Member names in generated classes should not have prefixes 'm' before their names.
In the above example, the private member name would be 'value' not 'mvalue' as it is done
now.
> 4. Convert getters and setters to have CamelCase. e.g. in the above example the getter
will be:
>   public Buffer getValue();
> 5. Provide a 'swiggable' C binding, so that processing the generated C code with swig
allows it to be used in scripting languages such as Python and Perl.
> 6. The default --language="java" target would generate class code for records that would
not have Hadoop dependency on WritableComparable interface, but instead would have "implements
Record, Comparable". (i.e. It will not have write() and readFields() methods.) An additional
option "--writable" will need to be specified on rcc commandline to generate classes that
"implements Record, WritableComparable".
> 7. Optimize generated write() and readFields() methods, so that they do not have to create
BinaryOutputArchive or BinaryInputArchive every time these methods are called on a record.
> 8. Implement ByteInStream and ByteOutStream for C++ runtime, as they will be needed for
using Hadoop Record I/O with forthcoming C++ MapReduce framework (currently, only FileStreams
are provided.)
> 9. Generate clone() methods for records in Java i.e. the generated classes should implement
Cloneable.
> 10. As part of Hadoop build process, produce a tar bundle for Record I/O alone. This
tar bundle will contain the translator classes and ant task (lib/rcc.jar), translator script
(bin/rcc), Java runtime (recordio.jar) that includes org.apache.hadoop.record.*, sources for
the java runtime (src/java), and c/c++ runtime sources with Makefiles (src/c++, src/c).
> 11. Make generated Java codes for maps and vectors use Java generics.
> These are the proposed user-visible changes. Internally, the translator will be restructured
so that it is easier to plug-in translators for different targets.

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