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/
optimize.go
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/
optimize.go
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// Copyright 2016 The Cockroach Authors.
//
// 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,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
// implied. See the License for the specific language governing
// permissions and limitations under the License.
//
// Author: Raphael 'kena' Poss (knz@cockroachlabs.com)
package sql
import "github.com/cockroachdb/cockroach/pkg/sql/parser"
// optimizePlan transforms the query plan into its final form. This
// includes calling expandPlan(). The SQL "prepare" phase, as well as
// the EXPLAIN statement, should merely build the plan node(s) and
// call optimizePlan(). This is called automatically by makePlan().
func (p *planner) optimizePlan(plan planNode, needed []bool) error {
// We propagate the needed columns a first time. This will remove
// any unused renders, which in turn may simplify expansion (remove
// sub-expressions).
setNeededColumns(plan, needed)
// Perform plan expansion; this does index selection, sort
// optimization etc.
if err := p.expandPlan(plan); err != nil {
return err
}
// We now propagate the needed columns again. This will ensure that
// the needed columns are properly computed for newly expanded nodes.
setNeededColumns(plan, needed)
// Now do the same work for all sub-queries.
i := subqueryInitializer{p: p}
v := planVisitor{p: p, observer: &i}
v.visit(plan)
return i.err
}
// subqueryInitializer ensures that initNeededColumns() and
// optimizeFilters() is called on the planNodes of all sub-query
// expressions.
type subqueryInitializer struct {
p *planner
err error
}
var _ planObserver = &subqueryInitializer{}
var _ parser.Visitor = &subqueryInitializer{}
// expr implements the planObserver interface.
func (i *subqueryInitializer) expr(_, _ string, _ int, expr parser.Expr) {
if expr == nil || i.err != nil {
return
}
parser.WalkExprConst(i, expr)
}
func (i *subqueryInitializer) enterNode(_ string, _ planNode) bool { return true }
func (i *subqueryInitializer) leaveNode(_ string) {}
func (i *subqueryInitializer) attr(_, _, _ string) {}
// VisitPre implements the parser.Visitor interface.
func (i *subqueryInitializer) VisitPre(expr parser.Expr) (recurse bool, newExpr parser.Expr) {
if i.err != nil {
return false, expr
}
if sq, ok := expr.(*subquery); ok && sq.plan != nil {
needed := make([]bool, len(sq.plan.Columns()))
if sq.execMode != execModeExists {
// EXISTS does not need values; the rest does.
for i := range needed {
needed[i] = true
}
}
if err := i.p.optimizePlan(sq.plan, needed); err != nil {
i.err = err
}
sq.expanded = true
return false, expr
}
return true, expr
}
// VisitPost implements the parser.Visitor interface.
func (i *subqueryInitializer) VisitPost(expr parser.Expr) parser.Expr { return expr }