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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 21:22:05 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12475653
] 

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

> the generated code is much larger

In this tradeoff between larger code size and smaller source code, I choose smaller source
code.

> Writable imposes a single format.

Writable and WritableComparable are for high-performance binary i/o and comparison.  Records
support other, non-binary representations.  Applications that require the highest-performance
binary format can use the Writable methods.  Applications that desire format flexibility can
use the other interface.  If record's other binary i/o implementation is efficient enough,
then it could be implemented on the base Record class, with no separate Writable or WritableComparable
methods implemented per generated class.  If it is as performant and more general, perhaps
it should replace Writable and WritableComparable.  But if, on the other hand, we can generate
significantly higher-performance implementations of the Writable and WritableComparable API,
then we should generate these per-class implementations, and all applications can choose.

The description of this issue lists 11 changes.  I object to one of them.  I have done so
since before any code was written, so this is not a surprise.  I'm somewhat surprised that
my concerns have been ignored.  The constructive thing to do at this point is to make a patch
without that one item, then perhaps pursue that separately.  Apache operates by consensus
and merit.  I do not see the merit of that change.

> 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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