Github user kiszk commented on a diff in the pull request:
https://github.com/apache/spark/pull/20153#discussion_r161362308
--- Diff:
sql/core/src/main/java/org/apache/spark/sql/sources/v2/reader/SupportsScanColumnarBatch.java
---
@@ -0,0 +1,51 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.sources.v2.reader;
+
+import java.util.List;
+
+import org.apache.spark.annotation.InterfaceStability;
+import org.apache.spark.sql.Row;
+import org.apache.spark.sql.vectorized.ColumnarBatch;
+
+/**
+ * A mix-in interface for {@link DataSourceV2Reader}. Data source readers
can implement this
+ * interface to output {@link ColumnarBatch} and make the scan faster.
+ */
+@InterfaceStability.Evolving
+public interface SupportsScanColumnarBatch extends DataSourceV2Reader {
+ @Override
+ default List<ReadTask<Row>> createReadTasks() {
+ throw new IllegalStateException(
+ "createReadTasks should not be called with
SupportsScanColumnarBatch.");
+ }
+
+ /**
+ * Similar to {@link DataSourceV2Reader#createReadTasks()}, but returns
columnar data in batches.
+ */
+ List<ReadTask<ColumnarBatch>> createBatchReadTasks();
+
+ /**
+ * A safety door for columnar batch reader. It's possible that the
implementation can only support
+ * some certain columns with certain types. Users can overwrite this
method and
+ * {@link #createReadTasks()} to fallback to normal read path under some
conditions.
+ */
+ default boolean enableBatchRead() {
--- End diff --
I see. It would be good to clarify it in the comment.
For example, Is this true? `A safety door for [[ColumnarBatch]] reader.`
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