spark技术分享MultiInstanceRelation
MultiInstanceRelation is a contact of logical operators which a single instance might appear multiple times in a logical query plan.
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package org.apache.spark.sql.catalyst.analysis trait MultiInstanceRelation { def newInstance(): LogicalPlan } |
When ResolveReferences logical evaluation is executed, every MultiInstanceRelation in a logical query plan is requested to produce a new version of itself with globally unique expression ids.
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