LogicalPlanVisitor — Base Visitor for Computing Statistics of Logical Plan-spark技术分享

LogicalPlanVisitor — Contract for Computing Statistic Estimates and Query Hints of Logical Plan

LogicalPlanVisitor is the contract that uses the visitor design pattern to scan a logical query plan and compute estimates of plan statistics and query hints.

Tip	Read about the visitor design pattern in Wikipedia.

LogicalPlanVisitor defines visit method that dispatches computing the statistics of a logical plan to the corresponding handler methods.



visit(p: LogicalPlan): T

visit(p: LogicalPlan): T

Note	`T` stands for the type of a result to be computed (while visiting the query plan tree) and is currently always Statistics only.

The concrete LogicalPlanVisitor is chosen per spark.sql.cbo.enabled configuration property. When turned on (i.e. true), LogicalPlanStats uses BasicStatsPlanVisitor while SizeInBytesOnlyStatsPlanVisitor otherwise.

Note	spark.sql.cbo.enabled configuration property is off, i.e. `false` by default.

Table 1. LogicalPlanVisitors
LogicalPlanVisitor	Description
BasicStatsPlanVisitor
SizeInBytesOnlyStatsPlanVisitor