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https://issues.apache.org/jira/browse/HADOOP-941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12475586
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Milind Bhandarkar commented on HADOOP-941:
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>Since one of the uses that is being considered is for a wire protocol, that is
>precisely what makes Writable and
WritableComparable valuable.
Unfortunately, Writable imposes a single format. Ås it is currently in Hadoop,
Writable implies Binary (not-so packed Binary) format. From the users'
experience, just by changing the format as a string in the record i/o
interface, they can output csv or xml, other common formats (pluggable, JSON as
a possible candidate), with the advantage that they are readable and therefore
more debuggable. If Writable interface allowed us to specify a different
serialization method, it would not be as indecipherable as it is now.
The Record interface, which has more readable "serialize" and "deserialize"
methods rather than "write" and "readFields" (i.e. binary) were to replace
Writable completely, it would be good for Hadoop long-term.
e.g. Then all the popular formats, e.g. Text, Binary, and XML will all be
interpretable through a single interface.
Maybe we can use this dicussion for a better cause. To fix the problems in the
Hadoop development process itself. This proposal has been on Jira for one whole
month. Asking for input from users and other stake holders. And after
significant efforts spent on implementation, this minor issue has come to the
fore. What bothers me is the failure of the process, not so much of the wasted
efforts. We need to learn from this, so that we avoid such happenings in the
future. How can we improve this process ?
> 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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