Github user jose-torres commented on a diff in the pull request:
https://github.com/apache/spark/pull/22009#discussion_r209013149
--- Diff:
sql/core/src/main/java/org/apache/spark/sql/sources/v2/reader/PartitionReaderFactory.java
---
@@ -0,0 +1,68 @@
+/*
+ * 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.io.Serializable;
+
+import org.apache.spark.annotation.InterfaceStability;
+import org.apache.spark.sql.catalyst.InternalRow;
+import org.apache.spark.sql.vectorized.ColumnarBatch;
+
+/**
+ * A factory used to create {@link PartitionReader} instances.
+ */
[email protected]
+public interface PartitionReaderFactory extends Serializable {
+
+ /**
+ * Returns a row-based partition reader to read data from the given
{@link InputPartition}.
+ *
+ * Implementations probably need to cast the input partition to the
concrete
+ * {@link InputPartition} class defined for the data source.
+ *
+ * If this method fails (by throwing an exception), the corresponding
Spark task would fail and
+ * get retried until hitting the maximum retry times.
+ */
+ PartitionReader<InternalRow> createReader(InputPartition partition);
+
+ /**
+ * Returns a columnar partition reader to read data from the given
{@link InputPartition}.
+ *
+ * Implementations probably need to cast the input partition to the
concrete
+ * {@link InputPartition} class defined for the data source.
+ *
+ * If this method fails (by throwing an exception), the corresponding
Spark task would fail and
+ * get retried until hitting the maximum retry times.
+ */
+ default PartitionReader<ColumnarBatch>
createColumnarReader(InputPartition partition) {
+ throw new UnsupportedOperationException("Cannot create columnar
reader.");
+ }
+
+ /**
+ * Returns true if the given {@link InputPartition} should be read by
Spark in a columnar way.
+ * This means, implementations must also implement {@link
#createColumnarReader(InputPartition)}
+ * for the input partitions that this method returns true.
+ *
+ * As of Spark 2.4, Spark can only read all input partition in a
columnar way, or none of them.
+ * Data source can't mix columnar and row-based partitions. This will be
relaxed in future
--- End diff --
nit: may be relaxed, we shouldn't guarantee it
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