package org.apache.spark.sql.catalyst.rules
abstract class Rule[TreeType <: TreeNode[_]] {
// only required properties (vals and methods) that have no implementation
// the others follow
def apply(plan: TreeType): TreeType
}Catalyst Rule — Named Transformation of TreeNodes
Rule is a named transformation that can be applied to (i.e. executed on or transform) a TreeNode to produce a new TreeNode.
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Note
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TreeType is the type of the TreeNode implementation that a Rule can be applied to, i.e. LogicalPlan, SparkPlan or Expression or a combination thereof.
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Rule has a rule name (that is the class name of a rule).
ruleName: StringRule is mainly used to create a batch of rules for a RuleExecutor.
The other notable use cases of Rule are as follows:
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When
ExperimentalMethodsis requested for extraOptimizations -
When
BaseSessionStateBuilderis requested for customResolutionRules, customPostHocResolutionRules, customOperatorOptimizationRules, and the Optimizer -
When
Analyzeris requested for extendedResolutionRules and postHocResolutionRules (see BaseSessionStateBuilder and HiveSessionStateBuilder) -
When
Optimizeris requested for extendedOperatorOptimizationRules -
When
QueryExecutionis requested for preparations