Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/19424#discussion_r144233678
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/DataSourceReaderHolder.scala
---
@@ -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.execution.datasources.v2
+
+import java.util.Objects
+
+import org.apache.spark.sql.catalyst.expressions.{Attribute,
AttributeReference}
+import org.apache.spark.sql.sources.v2.reader._
+
+/**
+ * A base class for data source reader holder with customized
equals/hashCode methods.
+ */
+trait DataSourceReaderHolder {
+
+ /**
+ * The full output of the data source reader, without column pruning.
+ */
+ def fullOutput: Seq[AttributeReference]
+
+ /**
+ * The held data source reader.
+ */
+ def reader: DataSourceV2Reader
+
+ /**
+ * The metadata of this data source reader that can be used for equality
test.
+ */
+ private def metadata: Seq[Any] = {
+ val filters: Any = reader match {
+ case s: SupportsPushDownCatalystFilters =>
s.pushedCatalystFilters().toSet
+ case s: SupportsPushDownFilters => s.pushedFilters().toSet
+ case _ => Nil
+ }
+ Seq(fullOutput, reader.getClass, reader.readSchema(), filters)
+ }
+
+ def canEqual(other: Any): Boolean
+
+ override def equals(other: Any): Boolean = other match {
+ case other: DataSourceReaderHolder =>
+ canEqual(other) && metadata.length == other.metadata.length &&
+ metadata.zip(other.metadata).forall { case (l, r) => l == r }
+ case _ => false
+ }
+
+ override def hashCode(): Int = {
+ metadata.map(Objects.hashCode).foldLeft(0)((a, b) => 31 * a + b)
+ }
+
+ lazy val output: Seq[Attribute] = reader.readSchema().map(_.name).map {
name =>
+ fullOutput.find(_.name == name).get
--- End diff --
Shall we use resolver instead of string comparison?
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