74 lines
2.0 KiB
Go
74 lines
2.0 KiB
Go
// Copyright 2017 PingCAP, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package plan
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import (
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"github.com/pingcap/tidb/ast"
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"github.com/pingcap/tidb/expression"
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)
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// Cacheable checks whether the input ast is cacheable.
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func Cacheable(node ast.Node) bool {
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if _, isSelect := node.(*ast.SelectStmt); !isSelect {
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return false
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}
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checker := cacheableChecker{
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cacheable: true,
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}
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node.Accept(&checker)
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return checker.cacheable
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}
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// cacheableChecker checks whether a query's plan can be cached, querys that:
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// 1. have ExistsSubqueryExpr, or
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// 2. have VariableExpr
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// will not be cached currently.
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// NOTE: we can add more rules in the future.
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type cacheableChecker struct {
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cacheable bool
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}
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// Enter implements Visitor interface.
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func (checker *cacheableChecker) Enter(in ast.Node) (out ast.Node, skipChildren bool) {
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switch node := in.(type) {
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case *ast.VariableExpr, *ast.ExistsSubqueryExpr:
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checker.cacheable = false
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return in, true
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case *ast.FuncCallExpr:
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if _, found := expression.UnCacheableFunctions[node.FnName.L]; found {
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checker.cacheable = false
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return in, true
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}
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case *ast.Limit:
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if node.Count != nil {
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if _, isParamMarker := node.Count.(*ast.ParamMarkerExpr); isParamMarker {
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checker.cacheable = false
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return in, true
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}
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}
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if node.Offset != nil {
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if _, isParamMarker := node.Offset.(*ast.ParamMarkerExpr); isParamMarker {
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checker.cacheable = false
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return in, true
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}
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}
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}
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return in, false
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}
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// Leave implements Visitor interface.
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func (checker *cacheableChecker) Leave(in ast.Node) (out ast.Node, ok bool) {
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return in, checker.cacheable
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}
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