Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/21118#discussion_r183380926
--- Diff:
sql/core/src/main/java/org/apache/spark/sql/sources/v2/reader/SupportsScanUnsafeRow.java
---
@@ -1,46 +0,0 @@
-/*
- * 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.catalyst.expressions.UnsafeRow;
-
-/**
- * A mix-in interface for {@link DataSourceReader}. Data source readers
can implement this
- * interface to output {@link UnsafeRow} directly and avoid the row copy
at Spark side.
- * This is an experimental and unstable interface, as {@link UnsafeRow} is
not public and may get
- * changed in the future Spark versions.
- */
-@InterfaceStability.Unstable
-public interface SupportsScanUnsafeRow extends DataSourceReader {
--- End diff --
I think we still need this trait.
In Spark SQL there is a contract that all operators produce `UnsafeRow`,
except some Dataset related operators. We have operators assuming the input
rows are `UnsafeRow` and do type cast, e.g. operators which use
`GenerateUnsafeRowJoiner`.
That is to say, the data source scan has to do an unsafe projection to make
sure it produces unsafe rows. This will be a waste if the data source already
produces unsafe rows.
For file-based data source, we solve this issue by adding a flag
`needsUnsafeRowConversion` to decide if we need the unsafe projection or not.
Another solution is what @rdblue proposed in the dev list discussion: do
`isInstanOf[UnsafeRow]` check for each input row and skip unsafe projection if
it's already unsafe row. That may have a performance penalty because of the
per-row check.
So this trait is still useful, at least for the built-in file-based data
sources.
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