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Re: [Fwd: [Apache Beam] Custom DataSourceV2 instanciation: parameters passing and Encoders]


Hi everyone, 

Does anyone have comments on this question?

Thanks
Etienne

Le vendredi 14 décembre 2018 à 10:37 +0100, Etienne Chauchot a écrit :
Hi guys,
I'm currently coding a POC on a new spark runner based on structured streaming and new DataSourceV2 API and I'm having an interrogation. Having found no pointers on the internet, I've asked the spark community with no luck. If anyone of you have knowledge about new Spark DataSourceV2 API, can you share thoughts?

Also I did not mention in the email but I did not find any way to get a reference on the automatically created DataSourceV2 instance, so I cannot lazy init the source either.

Thanks

Etienne

-------- Message transféré --------
De: Etienne Chauchot <echauchot@xxxxxxxxxx>
Objet: [Apache Beam] Custom DataSourceV2 instanciation: parameters passing and Encoders
Date: Tue, 11 Dec 2018 19:02:23 +0100

Hi Spark guys,

I'm Etienne Chauchot and I'm a committer on the Apache Beam project.

We have what we call runners. They are pieces of software that translate pipelines written using Beam API into pipelines that use native execution engine API. Currently, the Spark runner uses old RDD / DStream APIs.
I'm writing a new runner that will use structured streaming (but not continuous processing, and also no schema for now).

I am just starting. I'm currently trying to map our sources to yours. I'm targeting new DataSourceV2 API. It maps pretty well with Beam sources but I have a problem with instanciation of the custom source.
I searched for an answer in stack-overflow and user ML with no luck. I guess it is a too specific question:

When visiting Beam DAG I have access to Beam objects such as Source and Reader that I need to map to MicroBatchReader and InputPartitionReader.
As far as I understand, a custom DataSourceV2 is instantiated automatically by spark thanks to sparkSession.readStream().format(providerClassName) or similar code. The problem is that I can only pass options of primitive types + String so I cannot pass the Beam Source to DataSourceV2.
=> Is there a way to do so ?


Also I get as an output a Dataset<Row>. The Row contains an instance of Beam WindowedValue<T>, T is the type parameter of the Source. I do a map on the Dataset to transform it to a Dataset<WindowedValue<T>>. I have a question related to the Encoder: 
=> how to properly create an Encoder for the generic type WindowedValue<T> to use in the map?

Here is the code:

And more specially:

Thanks,

Etienne