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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 Mon, 26 Feb 2007 17:33:06 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12475916
] 

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

> dependency on the Lucene jar. Which was deemed unacceptable, so we copied Lucene's PriorityQueue

I didn't like that change, since it duplicated code.  But the duplication was across projects,
and thus harder to avoid, and it fixed a serious bug, that Hadoop-based applications that
wanted to use a different version of Lucene from the one in Hadoop could not easily do so,
as the version included in Hadoop was found first on the class path.  So the cost seemed worth
the benefit.  But here I don't see any serious functional bug that implementing Writable and
WritableComparable causes.  Perhaps, somewhere down the line, such a bug will emerge, and
we'll take on what source-code complexity is required to fix it then.  But, perhaps again,
we'll never have to.  Let's wait and see.  None of the arguments I have heard (package names,
generated code size, jar file size) yet constitute bugs worthy of fixing unless the cost of
the fix is negligible.  The record code generation is likely to get more complex as time passes,
to add features that fix real problems.  Making it more complex now has a combinatorial effect
on our ability to maintain this code: more conditional branches to edit, more modes to test,
more features to document, etc.  The long-term cost of adding code complexity are much greater
than, e.g., the long-term costs of slightly larger generated code size.

> 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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