I am using v2.4.0-RC2

 

The code as is wouldn’t run (e.g. planBatchInputPartitions returns null). How are you calling it?

 

When I do:

Val df = spark.read.format(mypackage).load().show()

I am getting a single creation, how are you creating the reader?

 

Thanks,

        Assaf

 

From: Shubham Chaurasia [mailto:shubh.chaurasia@gmail.com]
Sent: Tuesday, October 9, 2018 2:02 PM
To: Mendelson, Assaf; user@spark.apache.org
Subject: Re: DataSourceV2 APIs creating multiple instances of DataSourceReader and hence not preserving the state

 

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Thanks Assaf, you tried with tags/v2.4.0-rc2?

 

Full Code:

 

MyDataSource is the entry point which simply creates Reader and Writer

 

public class MyDataSource implements DataSourceV2, WriteSupport, ReadSupport, SessionConfigSupport {

 

  @Override public DataSourceReader createReader(DataSourceOptions options) {

    return new MyDataSourceReader(options.asMap());

  }

 

  @Override

  public Optional<DataSourceWriter> createWriter(String jobId, StructType schema,

      SaveMode mode, DataSourceOptions options) {

    // creates a dataSourcewriter here..

    return Optional.of(dataSourcewriter);

  }

 

  @Override public String keyPrefix() {

    return "myprefix";

  }

 

}

 

public class MyDataSourceReader implements DataSourceReader, SupportsScanColumnarBatch {

 

  StructType schema = null;

  Map<String, String> options;

 

  public MyDataSourceReader(Map<String, String> options) {

    System.out.println("MyDataSourceReader.MyDataSourceReader: Instantiated...." + this);

    this.options = options;

  }

 

  @Override

  public List<InputPartition<ColumnarBatch>> planBatchInputPartitions() {

    //variable this.schema is null here since readSchema() was called on a different instance

    System.out.println("MyDataSourceReader.planBatchInputPartitions: " + this + " schema: " + this.schema);

    //more logic......

    return null;

  }

 

  @Override

  public StructType readSchema() {

    //some logic to discover schema

    this.schema = (new StructType())

        .add("col1", "int")

        .add("col2", "string");

    System.out.println("MyDataSourceReader.readSchema: " + this + " schema: " + this.schema);

    return this.schema;

  }

}

 

Thanks,

Shubham

 

On Tue, Oct 9, 2018 at 3:59 PM Mendelson, Assaf <Assaf.Mendelson@rsa.com> wrote:

Could you add a fuller code example? I tried to reproduce it in my environment and I am getting just one instance of the reader…

 

Thanks,

        Assaf

 

From: Shubham Chaurasia [mailto:shubh.chaurasia@gmail.com]
Sent: Tuesday, October 9, 2018 9:31 AM
To: user@spark.apache.org
Subject: DataSourceV2 APIs creating multiple instances of DataSourceReader and hence not preserving the state

 

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Please report any suspicious attachments, links, or requests for sensitive information.

Hi All,

 

--Spark built with tags/v2.4.0-rc2

 

Consider following DataSourceReader implementation:

 

public class MyDataSourceReader implements DataSourceReader, SupportsScanColumnarBatch {

  StructType
schema = null;
  Map<String, String>
options;

 
public MyDataSourceReader(Map<String, String> options) {
    System.
out.println("MyDataSourceReader.MyDataSourceReader: Instantiated...." + this);
   
this.options = options;
  }

 
@Override
 
public List<InputPartition<ColumnarBatch>> planBatchInputPartitions() {
   
//variable this.schema is null here since readSchema() was called on a different instance
   
System.out.println("MyDataSourceReader.planBatchInputPartitions: " + this + " schema: " + this.schema);
   
//more logic......
   
return null;
  }

 
@Override
 
public StructType readSchema() {
   
//some logic to discover schema
   
this.schema = (new StructType())
        .add(
"col1", "int")
        .add(
"col2", "string");
    System.
out.println("MyDataSourceReader.readSchema: " + this + " schema: " + this.schema);
   
return this.schema;
  }
}
1) First readSchema() is called on MyDataSourceReader@instance1 which sets class variable schema.
2) Now when planBatchInputPartitions() is called, it is being called on a different instance of MyDataSourceReader and hence I am not getting the value of schema in method planBatchInputPartitions().
 
How can I get value of schema which was set in readSchema() method, in planBatchInputPartitions() method?
 
Console Logs:
 
scala> mysource.executeQuery("select * from movie").show
 
MyDataSourceReader.MyDataSourceReader: Instantiated....MyDataSourceReader@59ea8f1b
MyDataSourceReader.readSchema: MyDataSourceReader@59ea8f1b schema: StructType(StructField(col1,IntegerType,true), StructField(col2,StringType,true))
MyDataSourceReader.MyDataSourceReader: Instantiated....MyDataSourceReader@a3cd3ff
MyDataSourceReader.planBatchInputPartitions: MyDataSourceReader@a3cd3ff schema: null

 

Thanks,

Shubham