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From "Benjamin Reed (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-941) Make Hadoop Record I/O Easier to use outside Hadoop
Date Sat, 27 Jan 2007 19:26:49 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12468058
] 

Benjamin Reed commented on HADOOP-941:
--------------------------------------

I will admit to being one of the motivators of this bug. We have found record io extremely
useful in applications that have nothing to do with Hadoop. (We use it in a message passing
layer and to maintain a "database" log as well as serialize the contents of the "database".)
Currently we maintain a separate customized copy of the record io code, but it seems very
counter productive if everyone who wants to use record io does this.

I can see this easily becoming a very useful part of Hadoop in its own right (much as Hadoop
is a useful part of Nutch in its own right) since generic cross language cross encoding record
layers seem hard to come by for some reason. As it is, developers are going to be very hesitant
to use record io outside of Hadoop because Hadoop developers could change things (such as
introduce more dependencies on other parts of Hadoop).

It is very simple to use the --writable flag Milind proposes or even make record io stand
alone and have a simple RecordWritable class that Hadoop uses to interface to record io.

Implementing these changes and making it possible to build just a recordio.jar will allow
developers to realize that they can use record io in their project rather than reinvent the
wheel.

> 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
>             Fix For: 0.11.0
>
>
> 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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