Alright, so it is a big project which uses a SQL store underneath.
I extracted out the minimal code and made a smaller project out of it and
still it is creating multiple instances.
Here is my project:
├── my-datasource.iml
├── pom.xml
├── src
│ ├── main
│ │ ├── java
│ │ │ └── com
│ │ │ └── shubham
│ │ │ ├── MyDataSource.java
│ │ │ └── reader
│ │ │ └── MyDataSourceReader.java
MyDataSource.java
-------------------------------------------------
package com.shubham;
import com.shubham.reader.MyDataSourceReader;
import org.apache.spark.sql.SaveMode;
import org.apache.spark.sql.sources.v2.DataSourceOptions;
import org.apache.spark.sql.sources.v2.DataSourceV2;
import org.apache.spark.sql.sources.v2.ReadSupport;
import org.apache.spark.sql.sources.v2.WriteSupport;
import org.apache.spark.sql.sources.v2.reader.DataSourceReader;
import org.apache.spark.sql.sources.v2.writer.DataSourceWriter;
import org.apache.spark.sql.types.StructType;
import java.util.Optional;
public class MyDataSource implements DataSourceV2, ReadSupport, WriteSupport {
public DataSourceReader createReader(DataSourceOptions options) {
System.out.println("MyDataSource.createReader: Going to create a
new MyDataSourceReader");
return new MyDataSourceReader(options.asMap());
}
public Optional<DataSourceWriter> createWriter(String writeUUID,
StructType schema, SaveMode mode, DataSourceOptions options) {
return Optional.empty();
}
}
MyDataSourceReader.java
-------------------------------------------------
package com.shubham.reader;
import org.apache.spark.sql.sources.v2.reader.DataSourceReader;
import org.apache.spark.sql.sources.v2.reader.InputPartition;
import org.apache.spark.sql.sources.v2.reader.SupportsScanColumnarBatch;
import org.apache.spark.sql.types.StructType;
import org.apache.spark.sql.vectorized.ColumnarBatch;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
public class MyDataSourceReader implements DataSourceReader,
SupportsScanColumnarBatch {
private Map<String, String> options;
private StructType schema;
public MyDataSourceReader(Map<String, String> options) {
System.out.println("MyDataSourceReader.MyDataSourceReader:
Instantiated...." + this);
this.options = options;
}
@Override
public StructType readSchema() {
this.schema = (new StructType())
.add("col1", "int")
.add("col2", "string");
System.out.println("MyDataSourceReader.readSchema: " + this + "
schema: " + this.schema);
return this.schema;
}
@Override
public List<InputPartition<ColumnarBatch>> planBatchInputPartitions() {
System.out.println("MyDataSourceReader.planBatchInputPartitions: "
+ this + " schema: " + this.schema);
return new ArrayList<>();
}
}
----------------------------------------
spark-shell output
----------------------------------------
scala> spark.read.format("com.shubham.MyDataSource").option("query",
"select * from some_table").load.show
MyDataSource.createReader: Going to create a new MyDataSourceReader
MyDataSourceReader.MyDataSourceReader:
Instantiated....com.shubham.reader.MyDataSourceReader@69fa5536
MyDataSourceReader.readSchema:
com.shubham.reader.MyDataSourceReader@69fa5536 schema:
StructType(StructField(col1,IntegerType,true),
StructField(col2,StringType,true))
MyDataSource.createReader: Going to create a new MyDataSourceReader
MyDataSourceReader.MyDataSourceReader:
Instantiated....com.shubham.reader.MyDataSourceReader@3095c449
MyDataSourceReader.planBatchInputPartitions:
com.shubham.reader.MyDataSourceReader@3095c449 schema: null
+----+----+
|col1|col2|
+----+----+
+----+----+
Here 2 instances of reader, MyDataSourceReader@69fa5536 and
MyDataSourceReader@3095c449 are being created. Consequently schema is null
in MyDataSourceReader@3095c449.
Am I not doing it the correct way?
Thanks,
Shubham
On Tue, Oct 9, 2018 at 4:43 PM Mendelson, Assaf <assaf.mendel...@rsa.com>
wrote:
> 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.chaura...@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
>
>
>
> [EXTERNAL EMAIL]
> Please report any suspicious attachments, links, or requests for sensitive
> information.
>
> 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.mendel...@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.chaura...@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
>
>
>
> [EXTERNAL EMAIL]
> 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
>
>
>
>
