plan.go

// Copyright 2015 PingCAP, Inc.
//
// Licensed 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,
// See the License for the specific language governing permissions and
// limitations under the License.

package plan

import (
	"bytes"
	"encoding/json"
	"fmt"

	"github.com/juju/errors"
	"github.com/pingcap/tidb/context"
	"github.com/pingcap/tidb/expression"
	"github.com/pingcap/tidb/util/codec"
	"github.com/pingcap/tidb/util/types"
)

// UseDAGPlanBuilder means we should use new planner and dag pb.
var UseDAGPlanBuilder = false

// Plan is the description of an execution flow.
// It is created from ast.Node first, then optimized by the optimizer,
// finally used by the executor to create a Cursor which executes the statement.
type Plan interface {
	// AddParent means appending a parent for plan.
	AddParent(parent Plan)
	// AddChild means appending a child for plan.
	AddChild(children Plan)
	// ReplaceParent means replacing a parent with another one.
	ReplaceParent(parent, newPar Plan) error
	// ReplaceChild means replacing a child with another one.
	ReplaceChild(children, newChild Plan) error
	// Get all the parents.
	Parents() []Plan
	// Get all the children.
	Children() []Plan
	// Set the schema.
	SetSchema(schema *expression.Schema)
	// Get the schema.
	Schema() *expression.Schema
	// Get the ID.
	ID() string
	// Get id allocator
	Allocator() *idAllocator
	// SetParents sets the parents for the plan.
	SetParents(...Plan)
	// SetChildren sets the children for the plan.
	SetChildren(...Plan)

	context() context.Context

	extractCorrelatedCols() []*expression.CorrelatedColumn
}

type columnProp struct {
	col  *expression.Column
	desc bool
}

func (c *columnProp) equal(nc *columnProp, ctx context.Context) bool {
	return c.col.Equal(nc.col, ctx) && c.desc == nc.desc
}

// requriedProp stands for the required order property by parents. It will be all asc or desc.
type requiredProp struct {
	cols []*expression.Column
	desc bool
}

func (p *requiredProp) isEmpty() bool {
	return len(p.cols) == 0
}

// getHashKey encodes prop to a unique key. The key will be stored in the memory table.
func (p *requiredProp) getHashKey() ([]byte, error) {
	datums := make([]types.Datum, 0, len(p.cols)*2+1)
	datums = append(datums, types.NewDatum(p.desc))
	for _, c := range p.cols {
		datums = append(datums, types.NewDatum(c.FromID), types.NewDatum(c.Position))
	}
	bytes, err := codec.EncodeValue(nil, datums...)
	return bytes, errors.Trace(err)
}

// String implements fmt.Stringer interface. Just for test.
func (p *requiredProp) String() string {
	return fmt.Sprintf("Prop{cols: %s, desc: %v}", p.cols, p.desc)
}

type requiredProperty struct {
	props      []*columnProp
	sortKeyLen int
	limit      *Limit
}

// getHashKey encodes a requiredProperty to a unique hash code.
func (p *requiredProperty) getHashKey() ([]byte, error) {
	datums := make([]types.Datum, 0, len(p.props)*3+1)
	datums = append(datums, types.NewDatum(p.sortKeyLen))
	for _, c := range p.props {
		datums = append(datums, types.NewDatum(c.desc), types.NewDatum(c.col.FromID), types.NewDatum(c.col.Index))
	}
	bytes, err := codec.EncodeValue(nil, datums...)
	return bytes, errors.Trace(err)
}

// String implements fmt.Stringer interface. Just for test.
func (p *requiredProperty) String() string {
	ret := "Prop{"
	for _, colProp := range p.props {
		ret += fmt.Sprintf("col: %s, desc %v, ", colProp.col, colProp.desc)
	}
	ret += fmt.Sprintf("}, Len: %d", p.sortKeyLen)
	if p.limit != nil {
		ret += fmt.Sprintf(", Limit: %d,%d", p.limit.Offset, p.limit.Count)
	}
	return ret
}

type physicalPlanInfo struct {
	p     PhysicalPlan
	cost  float64
	count float64
}

// LogicalPlan is a tree of logical operators.
// We can do a lot of logical optimizations to it, like predicate pushdown and column pruning.
type LogicalPlan interface {
	Plan

	// PredicatePushDown pushes down the predicates in the where/on/having clauses as deeply as possible.
	// It will accept a predicate that is an expression slice, and return the expressions that can't be pushed.
	// Because it might change the root if the having clause exists, we need to return a plan that represents a new root.
	PredicatePushDown([]expression.Expression) ([]expression.Expression, LogicalPlan, error)

	// PruneColumns prunes the unused columns.
	PruneColumns([]*expression.Column)

	// ResolveIndicesAndCorCols resolves the index for columns and initializes the correlated columns.
	ResolveIndicesAndCorCols()

	// convert2PhysicalPlan converts the logical plan to the physical plan.
	// It is called recursively from the parent to the children to create the result physical plan.
	// Some logical plans will convert the children to the physical plans in different ways, and return the one
	// with the lowest cost.
	convert2PhysicalPlan(prop *requiredProperty) (*physicalPlanInfo, error)

	// convert2NewPhysicalPlan converts the logical plan to the physical plan. It's a new interface.
	// It is called recursively from the parent to the children to create the result physical plan.
	// Some logical plans will convert the children to the physical plans in different ways, and return the one
	// with the lowest cost.
	convert2NewPhysicalPlan(prop *requiredProp) (taskProfile, error)

	// buildKeyInfo will collect the information of unique keys into schema.
	buildKeyInfo()

	// pushDownTopN will push down the topN or limit operator during logical optimization.
	pushDownTopN(topN *Sort) LogicalPlan
}

// PhysicalPlan is a tree of the physical operators.
type PhysicalPlan interface {
	json.Marshaler
	Plan

	// matchProperty calculates the cost of the physical plan if it matches the required property.
	// It's usually called at the end of convert2PhysicalPlan. Some physical plans do not implement it because there is
	// no property to match, these plans just do the cost calculation directly.
	// If the cost of the physical plan does not match the required property, the cost will be set to MaxInt64
	// so it will not be chosen as the result physical plan.
	// childrenPlanInfo are used to calculate the result cost of the plan.
	// The returned *physicalPlanInfo will be chosen as the final plan if it has the lowest cost.
	// For the lowest level *PhysicalTableScan and *PhysicalIndexScan, even though it doesn't have childPlanInfo, we
	// create an initial *physicalPlanInfo to pass the row count.
	matchProperty(prop *requiredProperty, childPlanInfo ...*physicalPlanInfo) *physicalPlanInfo

	// Copy copies the current plan.
	Copy() PhysicalPlan

	// attach2TaskProfile makes the current physical plan as the father of task's physicalPlan and updates the cost of
	// current task. If the child's task is cop task, some operator may close this task and return a new rootTask.
	attach2TaskProfile(...taskProfile) taskProfile
}

type baseLogicalPlan struct {
	basePlan *basePlan
	planMap  map[string]*physicalPlanInfo
	taskMap  map[string]taskProfile
}

type basePhysicalPlan struct {
	basePlan *basePlan
}

func (p *baseLogicalPlan) getTaskProfile(prop *requiredProp) (taskProfile, error) {
	key, err := prop.getHashKey()
	if err != nil {
		return nil, errors.Trace(err)
	}
	return p.taskMap[string(key)], nil
}

func (p *baseLogicalPlan) getPlanInfo(prop *requiredProperty) (*physicalPlanInfo, error) {
	key, err := prop.getHashKey()
	if err != nil {
		return nil, errors.Trace(err)
	}
	return p.planMap[string(key)], nil
}

func (p *baseLogicalPlan) convert2PhysicalPlan(prop *requiredProperty) (*physicalPlanInfo, error) {
	info, err := p.getPlanInfo(prop)
	if err != nil {
		return nil, errors.Trace(err)
	}
	if info != nil {
		return info, nil
	}
	if len(p.basePlan.children) == 0 {
		return &physicalPlanInfo{p: p.basePlan.self.(PhysicalPlan)}, nil
	}
	child := p.basePlan.children[0].(LogicalPlan)
	info, err = child.convert2PhysicalPlan(prop)
	if err != nil {
		return nil, errors.Trace(err)
	}
	info = addPlanToResponse(p.basePlan.self.(PhysicalPlan), info)
	return info, p.storePlanInfo(prop, info)
}

func (p *baseLogicalPlan) storeTaskProfile(prop *requiredProp, task taskProfile) error {
	key, err := prop.getHashKey()
	if err != nil {
		return errors.Trace(err)
	}
	p.taskMap[string(key)] = task
	return nil
}

func (p *baseLogicalPlan) storePlanInfo(prop *requiredProperty, info *physicalPlanInfo) error {
	key, err := prop.getHashKey()
	if err != nil {
		return errors.Trace(err)
	}
	newInfo := *info // copy it
	p.planMap[string(key)] = &newInfo
	return nil
}

func (p *baseLogicalPlan) buildKeyInfo() {
	for _, child := range p.basePlan.children {
		child.(LogicalPlan).buildKeyInfo()
	}
	if len(p.basePlan.children) == 1 {
		switch p.basePlan.self.(type) {
		case *Exists, *LogicalAggregation, *Projection:
			p.basePlan.schema.Keys = nil
		case *SelectLock:
			p.basePlan.schema.Keys = p.basePlan.children[0].Schema().Keys
		default:
			p.basePlan.schema.Keys = p.basePlan.children[0].Schema().Clone().Keys
		}
	} else {
		p.basePlan.schema.Keys = nil
	}
}

func newBasePlan(tp string, allocator *idAllocator, ctx context.Context, p Plan) *basePlan {
	return &basePlan{
		tp:        tp,
		allocator: allocator,
		id:        tp + allocator.allocID(),
		ctx:       ctx,
		self:      p,
	}
}

func newBaseLogicalPlan(basePlan *basePlan) baseLogicalPlan {
	return baseLogicalPlan{
		planMap:  make(map[string]*physicalPlanInfo),
		taskMap:  make(map[string]taskProfile),
		basePlan: basePlan,
	}
}

func newBasePhysicalPlan(basePlan *basePlan) basePhysicalPlan {
	return basePhysicalPlan{
		basePlan: basePlan,
	}
}

func (p *basePhysicalPlan) matchProperty(prop *requiredProperty, childPlanInfo ...*physicalPlanInfo) *physicalPlanInfo {
	panic("You can't call this function!")
}

// PredicatePushDown implements LogicalPlan interface.
func (p *baseLogicalPlan) PredicatePushDown(predicates []expression.Expression) ([]expression.Expression, LogicalPlan, error) {
	if len(p.basePlan.children) == 0 {
		return predicates, p.basePlan.self.(LogicalPlan), nil
	}
	child := p.basePlan.children[0].(LogicalPlan)
	rest, _, err := child.PredicatePushDown(predicates)
	if err != nil {
		return nil, nil, errors.Trace(err)
	}
	if len(rest) > 0 {
		err = addSelection(p.basePlan.self, child, rest, p.basePlan.allocator)
		if err != nil {
			return nil, nil, errors.Trace(err)
		}
	}
	return nil, p.basePlan.self.(LogicalPlan), nil
}

func (p *basePlan) extractCorrelatedCols() []*expression.CorrelatedColumn {
	var corCols []*expression.CorrelatedColumn
	for _, child := range p.children {
		corCols = append(corCols, child.extractCorrelatedCols()...)
	}
	return corCols
}

func (p *basePlan) Allocator() *idAllocator {
	return p.allocator
}

// ResolveIndicesAndCorCols implements LogicalPlan interface.
func (p *baseLogicalPlan) ResolveIndicesAndCorCols() {
	for _, child := range p.basePlan.children {
		child.(LogicalPlan).ResolveIndicesAndCorCols()
	}
}

// PruneColumns implements LogicalPlan interface.
func (p *baseLogicalPlan) PruneColumns(parentUsedCols []*expression.Column) {
	if len(p.basePlan.children) == 0 {
		return
	}
	child := p.basePlan.children[0].(LogicalPlan)
	child.PruneColumns(parentUsedCols)
	p.basePlan.SetSchema(child.Schema())
}

// basePlan implements base Plan interface.
// Should be used as embedded struct in Plan implementations.
type basePlan struct {
	parents  []Plan
	children []Plan

	schema    *expression.Schema
	tp        string
	id        string
	allocator *idAllocator
	ctx       context.Context
	self      Plan
}

func (p *basePlan) copy() *basePlan {
	np := *p
	return &np
}

// MarshalJSON implements json.Marshaler interface.
func (p *basePlan) MarshalJSON() ([]byte, error) {
	children := make([]string, 0, len(p.children))
	for _, child := range p.children {
		children = append(children, child.ID())
	}
	childrenStrs, err := json.Marshal(children)
	if err != nil {
		return nil, errors.Trace(err)
	}
	buffer := bytes.NewBufferString("{")
	buffer.WriteString(fmt.Sprintf("\"children\": %s", childrenStrs))
	buffer.WriteString("}")
	return buffer.Bytes(), nil
}

// ID implements Plan ID interface.
func (p *basePlan) ID() string {
	return p.id
}

// SetSchema implements Plan SetSchema interface.
func (p *basePlan) SetSchema(schema *expression.Schema) {
	p.schema = schema
}

// Schema implements Plan Schema interface.
func (p *basePlan) Schema() *expression.Schema {
	return p.schema
}

// AddParent implements Plan AddParent interface.
func (p *basePlan) AddParent(parent Plan) {
	p.parents = append(p.parents, parent)
}

// AddChild implements Plan AddChild interface.
func (p *basePlan) AddChild(child Plan) {
	p.children = append(p.children, child)
}

// ReplaceParent means replace a parent for another one.
func (p *basePlan) ReplaceParent(parent, newPar Plan) error {
	for i, par := range p.parents {
		if par.ID() == parent.ID() {
			p.parents[i] = newPar
			return nil
		}
	}
	return SystemInternalErrorType.Gen("ReplaceParent Failed!")
}

// ReplaceChild means replace a child with another one.
func (p *basePlan) ReplaceChild(child, newChild Plan) error {
	for i, ch := range p.children {
		if ch.ID() == child.ID() {
			p.children[i] = newChild
			return nil
		}
	}
	return SystemInternalErrorType.Gen("ReplaceChildren Failed!")
}

// Parents implements Plan Parents interface.
func (p *basePlan) Parents() []Plan {
	return p.parents
}

// Children implements Plan Children interface.
func (p *basePlan) Children() []Plan {
	return p.children
}

// SetParents implements Plan SetParents interface.
func (p *basePlan) SetParents(pars ...Plan) {
	p.parents = pars
}

// SetChildren implements Plan SetChildren interface.
func (p *basePlan) SetChildren(children ...Plan) {
	p.children = children
}

func (p *basePlan) context() context.Context {
	return p.ctx
}