rdblue commented on a change in pull request #23266: [SPARK-26313][SQL] move 
read related methods from Table to read related mix-in traits
URL: https://github.com/apache/spark/pull/23266#discussion_r240379095
 
 

 ##########
 File path: 
sql/core/src/main/java/org/apache/spark/sql/sources/v2/SupportsBatchRead.java
 ##########
 @@ -20,14 +20,27 @@
 import org.apache.spark.annotation.Evolving;
 import org.apache.spark.sql.sources.v2.reader.Scan;
 import org.apache.spark.sql.sources.v2.reader.ScanBuilder;
+import org.apache.spark.sql.types.StructType;
 
 /**
- * An empty mix-in interface for {@link Table}, to indicate this table 
supports batch scan.
- * <p>
- * If a {@link Table} implements this interface, its {@link 
Table#newScanBuilder(DataSourceOptions)}
- * must return a {@link ScanBuilder} that builds {@link Scan} with {@link 
Scan#toBatch()}
- * implemented.
- * </p>
+ * A mix-in interface for {@link Table} to provide data reading ability of 
batch processing.
  */
 @Evolving
-public interface SupportsBatchRead extends Table { }
+public interface SupportsBatchRead extends Table {
+
+  /**
+   * Returns the schema of this table.
+   */
+  StructType schema();
+
+  /**
+   * Returns a {@link ScanBuilder} which can be used to build a {@link Scan} 
later. The built
+   * {@link Scan} must implement {@link Scan#toBatch()}. Spark will call this 
method for each data
+   * scanning query.
+   * <p>
+   * The builder can take some query specific information to do operators 
pushdown, and keep these
 
 Review comment:
   This doesn't need to explain how `ScanBuilder` works.

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