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From Micah Whitacre <mkwhita...@gmail.com>
Subject Re: Injecting alternate PType Converter implementations
Date Wed, 24 Apr 2013 23:02:46 GMT
> I think it's just that. It seems relatively low-risk to me (e.g., we
already use AvroKey in the AvroPairConverter for PTables).

Ok sounds good.  Do you want me to log a bug for this?

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

Yeah was going to look at it after Trevni.  It's Avro support is not as far
along (looks like ~16 days).  The goal was to hopefully help get support
for both into Crunch eventually and we can choose whichever is better for
our job.

On Wed, Apr 24, 2013 at 5:52 PM, Josh Wills <jwills@cloudera.com> wrote:

>
>
>
> 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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