spark UpdateAttributeNullability 源码
spark UpdateAttributeNullability 代码
文件路径：/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/UpdateAttributeNullability.scala
/*
* 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.catalyst.analysis
import org.apache.spark.sql.catalyst.expressions.Attribute
import org.apache.spark.sql.catalyst.plans.logical.{LeafNode, LogicalPlan}
import org.apache.spark.sql.catalyst.rules.Rule
import org.apache.spark.sql.catalyst.trees.AlwaysProcess
/**
* Updates nullability of Attributes in a resolved LogicalPlan by using the nullability of
* corresponding Attributes of its children output Attributes. This step is needed because
* users can use a resolved AttributeReference in the Dataset API and outer joins
* can change the nullability of an AttributeReference. Without this rule, a nullable column's
* nullable field can be actually set as non-nullable, which cause illegal optimization
* (e.g., NULL propagation) and wrong answers.
* See SPARK-13484 and SPARK-13801 for the concrete queries of this case.
*/
object UpdateAttributeNullability extends Rule[LogicalPlan] {
def apply(plan: LogicalPlan): LogicalPlan = plan.resolveOperatorsUpWithPruning(
AlwaysProcess.fn, ruleId) {
// Skip unresolved nodes.
case p if !p.resolved => p
// Skip leaf node, as it has no child and no need to update nullability.
case p: LeafNode => p
case p: LogicalPlan if p.childrenResolved =>
val nullabilities = p.children.flatMap(c => c.output).groupBy(_.exprId).map {
// If there are multiple Attributes having the same ExprId, we need to resolve
// the conflict of nullable field. We do not really expect this to happen.
case (exprId, attributes) => exprId -> attributes.exists(_.nullable)
}
// For an Attribute used by the current LogicalPlan, if it is from its children,
// we fix the nullable field by using the nullability setting of the corresponding
// output Attribute from the children.
p.transformExpressions {
case attr: Attribute if nullabilities.contains(attr.exprId) =>
attr.withNullability(nullabilities(attr.exprId))
}
}
}
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