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From Micah Whitacre <mkwhita...@gmail.com>
Subject Re: Injecting alternate PType Converter implementations
Date Wed, 24 Apr 2013 22:49:20 GMT
Is the change simply:

  private AvroWrapper<K> getWrapper() {
    if (wrapper == null) {
      // wrapper = new AvroWrapper<K>();
      wrapper = new AvroKey<K>();
    }
    return wrapper;
  }

Or are there more changes I might be missing?  Doing that got me past the
ClassCastException (though still trying to get my code working).

As I indicated I'm still just trying to prove out my code and if it pans
out we can probably wait till the 0.7.0 release (assuming the current ~2
month release cycle).  I'll leave it to you to evaluate the risk.

I'm guessing the injecting a converter issue will be more significant if I
try out the other Trevni format[1] where I'd need the converter to support
AvroValue instead of NullWritable.  So I'm fine with holding off a rushed
change before a release in lieu of a more holistic solution to both parts.

[1] -
http://avro.apache.org/docs/current/api/java/org/apache/trevni/avro/mapreduce/AvroTrevniKeyValueOutputFormat.html



On Wed, Apr 24, 2013 at 5:29 PM, Josh Wills <jwills@cloudera.com> wrote:

> Hey Micah,
>
> It seems like having the AvroKeyConverter use the AvroKey as the return
> type instead of AvroWrapper is the easiest way to solve this, since AvroKey
> is a subclass of AvroWrapper. That said, I agree, that's a thorny problem.
> We're just getting ready for the 0.6.0 release, but I'd be fine to get the
> switch in there if that solved this problem for you.
>
> J
>
>
> On Wed, Apr 24, 2013 at 3:23 PM, Micah Whitacre <mkwhitacre@gmail.com>wrote:
>
>> As an alternative to the standard AvroInput/OutputFormat, I've been
>> playing around with how to support alternate Avro file types like
>> Trevni[1], which give benefits when we want to only retrieve a subset of
>> the Avro object.
>>
>> Picking one of the implementations
>> (AvroTrevniKeyInputFormat/AvroTrevniKeyOutputFormat)[2], I implemented the
>> various Source/Target/SourceTarget implementations.  When I started trying
>> to test it out (to see if I did any of it right), I hit the issue that the
>> AvroKeyConverter only produces AvroWrapper objects and the output format
>> requires AvroKey.  So I get ClassCastExceptions CrunchOutputs.write(...)
>> method.
>>
>> Caused by: java.lang.ClassCastException:
>> org.apache.avro.mapred.AvroWrapper cannot be cast to
>> org.apache.avro.mapred.AvroKey
>> at
>> org.apache.trevni.avro.mapreduce.AvroTrevniKeyRecordWriter.write(AvroTrevniKeyRecordWriter.java:34)
>>  at org.apache.crunch.io.CrunchOutputs.write(CrunchOutputs.java:129)
>>
>> I was hoping that the target would be able to take any PCollection<?
>> extends AvroType> but it looks like I'd need to implement my own PType and
>> force consumers to use that just to change the converter to produce AvroKey
>> instead.
>>
>> Is implementing a custom PType the only way to inject an alternate
>> converter?  That seems like a high cost on the implementation side and
>> forcing a restriction onto others in the pipeline who are generally happy
>> with the standard AvroType and shouldn't be burdened with how the data
>> might be stored later on in the processing.
>>
>> Thoughts?
>>
>> [1] - http://avro.apache.org/docs/current/trevni/spec.html
>> [2] -
>> http://avro.apache.org/docs/current/api/java/org/apache/trevni/avro/mapreduce/AvroTrevniKeyOutputFormat.html
>>
>
>
>
> --
> Director of Data Science
> Cloudera <http://www.cloudera.com>
> Twitter: @josh_wills <http://twitter.com/josh_wills>
>

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