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From Josh Wills <jwi...@cloudera.com>
Subject Re: Injecting alternate PType Converter implementations
Date Wed, 24 Apr 2013 22:52:04 GMT
On Wed, Apr 24, 2013 at 3:49 PM, Micah Whitacre <mkwhitacre@gmail.com>wrote:

> 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 think it's just that. It seems relatively low-risk to me (e.g., we
already use AvroKey in the AvroPairConverter for PTables).


>
> 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
>

I'm also curious if you're looking at Parquet for this use case?


>
>
>
> 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>
>>
>
>


-- 
Director of Data Science
Cloudera <http://www.cloudera.com>
Twitter: @josh_wills <http://twitter.com/josh_wills>

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