optimizers

Documentation

Index

• Variables
• func Optimize(plan planners.IPlan, optimizers []Optimizer) planners.IPlan
• type Optimizer

Variables

var DefaultOptimizers = []Optimizer{

	ProjectPushDownOptimizer,

	PredicatePushDownOptimizer,
}

默认使用的优化器

var PredicatePushDownOptimizer = Optimizer{
	Name:        "PredicatePushDownOptimizer",
	Description: "Push predicates to scan plan",
	Reassembler: func(plan planners.IPlan) {
		var scan *planners.ScanPlan
		var filter *planners.FilterPlan

		visit := func(plan planners.IPlan) (kontinue bool, err error) {
			switch plan := plan.(type) {
			case *planners.ScanPlan:
				scan = plan
			case *planners.FilterPlan:
				filter = plan
			}
			return true, nil
		}
		if err := planners.Walk(visit, plan); err != nil {
			return
		}

		if scan != nil && filter != nil {
			scan.Filter = filter
		}
	},
}

PredicatePushDownOptimizer 谓词下推优化器，把filter条件往树上方移动

var ProjectPushDownOptimizer = Optimizer{
	Name:        "ProjectPushDownOptimizer",
	Description: "Push projects to scan plan",
	Reassembler: func(plan planners.IPlan) {
		var scan *planners.ScanPlan
		var project *planners.ProjectionPlan

		visit := func(plan planners.IPlan) (kontinue bool, err error) {
			switch plan := plan.(type) {
			case *planners.ScanPlan:
				scan = plan
			case *planners.ProjectionPlan:
				project = plan
			}
			return true, nil
		}
		if err := planners.Walk(visit, plan); err != nil {
			return
		}

		if scan != nil && project != nil {
			scan.Project = project
		}
	},
}

ProjectPushDownOptimizer 映射下推，不读取多余的列

Functions

func Optimize

func Optimize(plan planners.IPlan, optimizers []Optimizer) planners.IPlan

Types

type Optimizer

type Optimizer struct {

	// 优化器的名称
	Name string

	// 优化器的作用描述，但是似乎也没用到？
	Description string

	// 优化器的优化方法，对传入的执行计划做优化
	Reassembler func(planners.IPlan)
}

优化器的定义