486 lines
16 KiB
Go
486 lines
16 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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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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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 core
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import (
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"fmt"
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"github.com/pingcap/tidb/expression"
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"github.com/pingcap/tidb/infoschema"
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"github.com/pingcap/tidb/kv"
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"github.com/pingcap/tidb/parser/ast"
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"github.com/pingcap/tidb/parser/model"
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"github.com/pingcap/tidb/parser/mysql"
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"github.com/pingcap/tidb/sessionctx"
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driver "github.com/pingcap/tidb/types/parser_driver"
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"github.com/pingcap/tidb/util/logutil"
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"go.uber.org/zap"
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)
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// Cacheable checks whether the input ast(query) is cacheable with empty session context, which is mainly for testing.
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func Cacheable(node ast.Node, is infoschema.InfoSchema) bool {
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c, _ := CacheableWithCtx(nil, node, is)
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return c
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}
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// CacheableWithCtx checks whether the input ast(query) is cacheable.
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// Handle "ignore_plan_cache()" hint
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// If there are multiple hints, only one will take effect
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func CacheableWithCtx(sctx sessionctx.Context, node ast.Node, is infoschema.InfoSchema) (bool, string) {
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_, isSelect := node.(*ast.SelectStmt)
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_, isUpdate := node.(*ast.UpdateStmt)
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_, isInsert := node.(*ast.InsertStmt)
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_, isDelete := node.(*ast.DeleteStmt)
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_, isSetOpr := node.(*ast.SetOprStmt)
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if !(isSelect || isUpdate || isInsert || isDelete || isSetOpr) {
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return false, "not a SELECT/UPDATE/INSERT/DELETE/SET statement"
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}
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checker := cacheableChecker{
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sctx: sctx,
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cacheable: true,
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schema: is,
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}
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node.Accept(&checker)
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return checker.cacheable, checker.reason
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}
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// cacheableChecker checks whether a query can be cached:
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type cacheableChecker struct {
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sctx sessionctx.Context
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cacheable bool
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schema infoschema.InfoSchema
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reason string // reason why cannot use plan-cache
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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.SelectStmt:
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for _, hints := range node.TableHints {
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if hints.HintName.L == HintIgnorePlanCache {
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checker.cacheable = false
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checker.reason = "ignore plan cache by hint"
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return in, true
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}
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}
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case *ast.DeleteStmt:
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for _, hints := range node.TableHints {
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if hints.HintName.L == HintIgnorePlanCache {
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checker.cacheable = false
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checker.reason = "ignore plan cache by hint"
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return in, true
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}
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}
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case *ast.UpdateStmt:
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for _, hints := range node.TableHints {
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if hints.HintName.L == HintIgnorePlanCache {
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checker.cacheable = false
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checker.reason = "ignore plan cache by hint"
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return in, true
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}
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}
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case *ast.InsertStmt:
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if node.Select == nil {
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// do not cache insert-values-stmt like 'insert into t values (...)' since
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// no performance benefit and to save memory.
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checker.cacheable = false
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checker.reason = "ignore insert-values-stmt"
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return in, true
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}
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for _, hints := range node.TableHints {
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if hints.HintName.L == HintIgnorePlanCache {
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checker.cacheable = false
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checker.reason = "ignore plan cache by hint"
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return in, true
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}
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}
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case *ast.VariableExpr:
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checker.cacheable = false
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checker.reason = "query has user-defined variables is un-cacheable"
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return in, true
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case *ast.ExistsSubqueryExpr, *ast.SubqueryExpr:
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if !checker.sctx.GetSessionVars().EnablePlanCacheForSubquery {
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checker.cacheable = false
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checker.reason = "query has sub-queries is un-cacheable"
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return in, true
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}
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return in, false
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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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checker.reason = fmt.Sprintf("query has '%v' is un-cacheable", node.FnName.L)
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return in, true
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}
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case *ast.OrderByClause:
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for _, item := range node.Items {
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if _, isParamMarker := item.Expr.(*driver.ParamMarkerExpr); isParamMarker {
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checker.cacheable = false
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checker.reason = "query has 'order by ?' is un-cacheable"
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return in, true
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}
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}
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case *ast.GroupByClause:
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for _, item := range node.Items {
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if _, isParamMarker := item.Expr.(*driver.ParamMarkerExpr); isParamMarker {
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checker.cacheable = false
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checker.reason = "query has 'group by ?' is un-cacheable"
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return in, true
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}
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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.(*driver.ParamMarkerExpr); isParamMarker && !checker.sctx.GetSessionVars().EnablePlanCacheForParamLimit {
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checker.cacheable = false
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checker.reason = "query has 'limit ?' is un-cacheable"
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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.(*driver.ParamMarkerExpr); isParamMarker && !checker.sctx.GetSessionVars().EnablePlanCacheForParamLimit {
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checker.cacheable = false
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checker.reason = "query has 'limit ?, 10' is un-cacheable"
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return in, true
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}
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}
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case *ast.FrameBound:
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if _, ok := node.Expr.(*driver.ParamMarkerExpr); ok {
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checker.cacheable = false
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checker.reason = "query has ? in window function frames is un-cacheable"
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return in, true
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}
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case *ast.TableName:
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if checker.schema != nil {
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if isPartitionTable(checker.schema, node) {
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// Temporary disable prepared plan cache until https://github.com/pingcap/tidb/issues/33031
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// is fixed and additional tests with dynamic partition prune mode has been added.
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/*
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if checker.sctx != nil && checker.sctx.GetSessionVars().UseDynamicPartitionPrune() {
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return in, false // dynamic-mode for partition tables can use plan-cache
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}
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*/
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checker.cacheable = false
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checker.reason = "query accesses partitioned tables is un-cacheable"
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return in, true
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}
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if hasGeneratedCol(checker.schema, node) {
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checker.cacheable = false
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checker.reason = "query accesses generated columns is un-cacheable"
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return in, true
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}
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if isTempTable(checker.schema, node) {
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checker.cacheable = false
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checker.reason = "query accesses temporary tables is un-cacheable"
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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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// NonPreparedPlanCacheable checks whether the input ast is cacheable for non-prepared plan cache with empty session context, which is mainly for testing.
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func NonPreparedPlanCacheable(node ast.Node, is infoschema.InfoSchema) bool {
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ok, _ := NonPreparedPlanCacheableWithCtx(nil, node, is)
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return ok
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}
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// NonPreparedPlanCacheableWithCtx checks whether the input ast is cacheable for non-prepared plan cache.
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// Only support: select {field} from {single-table} where {cond} and {cond} ...
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// {cond}: {col} {op} {val}
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// {op}: >, <, =
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func NonPreparedPlanCacheableWithCtx(sctx sessionctx.Context, node ast.Node, is infoschema.InfoSchema) (ok bool, reason string) {
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selectStmt, isSelect := node.(*ast.SelectStmt)
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if !isSelect { // only support select statement now
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return false, "not a select statement"
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}
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if selectStmt.Kind != ast.SelectStmtKindSelect {
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return false, "not a select statement"
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}
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if len(selectStmt.TableHints) > 0 || // hints
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selectStmt.Distinct || selectStmt.GroupBy != nil || selectStmt.Having != nil || // agg
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selectStmt.WindowSpecs != nil || // window function
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selectStmt.OrderBy != nil || // order
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selectStmt.Limit != nil || // limit
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selectStmt.LockInfo != nil || selectStmt.SelectIntoOpt != nil { // lock info
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return false, "queries that have hints, aggregation, window-function, order-by, limit and lock are not supported"
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}
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from := selectStmt.From
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if from == nil || selectStmt.From.TableRefs == nil {
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return false, "queries that have sub-queries are not supported"
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}
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tableRefs := from.TableRefs
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if tableRefs.Right != nil {
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// We don't support the join for the non-prepared plan cache now.
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return false, "queries that access multiple tables are not supported"
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}
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switch x := tableRefs.Left.(type) {
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case *ast.TableSource:
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_, isTableName := x.Source.(*ast.TableName)
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if !isTableName {
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return false, "queries that have sub-queries are not supported"
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}
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}
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checker := nonPreparedPlanCacheableChecker{
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sctx: sctx,
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cacheable: true,
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schema: is,
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}
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node.Accept(&checker)
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return checker.cacheable, checker.reason
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}
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// nonPreparedPlanCacheableChecker checks whether a query's plan can be cached for non-prepared plan cache.
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// NOTE: we can add more rules in the future.
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type nonPreparedPlanCacheableChecker struct {
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sctx sessionctx.Context
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cacheable bool
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reason string // reason why this statement cannot hit the cache
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schema infoschema.InfoSchema
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tableNode *ast.TableName
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constCnt int // the number of constants/parameters in this query
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filterCnt int // the number of filters in the current node
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}
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// Enter implements Visitor interface.
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func (checker *nonPreparedPlanCacheableChecker) Enter(in ast.Node) (out ast.Node, skipChildren bool) {
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if checker.isFilterNode(in) {
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checker.filterCnt++
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}
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switch node := in.(type) {
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case *ast.SelectStmt, *ast.FieldList, *ast.SelectField, *ast.TableRefsClause, *ast.Join, *ast.BetweenExpr,
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*ast.TableSource, *ast.ColumnNameExpr, *ast.PatternInExpr:
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return in, !checker.cacheable // skip child if un-cacheable
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case *ast.ColumnName:
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if checker.filterCnt > 0 {
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// this column is appearing some filters, e.g. `col = 1`
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colType, found := getColType(checker.schema, checker.tableNode, node)
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if !found {
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checker.cacheable = false
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checker.reason = "some column is not found in table schema"
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} else if colType == mysql.TypeJSON || colType == mysql.TypeEnum || colType == mysql.TypeSet || colType == mysql.TypeBit {
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checker.cacheable = false
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checker.reason = "query has some filters with JSON, Enum, Set or Bit columns"
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}
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}
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return in, !checker.cacheable
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case *ast.BinaryOperationExpr:
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if _, found := expression.NonPreparedPlanCacheableOp[node.Op.String()]; !found {
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checker.cacheable = false
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checker.reason = "query has some unsupported binary operation"
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}
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return in, !checker.cacheable
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case *driver.ValueExpr:
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if node.IsNull() {
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// for a condition like `not-null-col = null`, the planner will optimize it to `False` and generate a
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// table-dual plan, but if it is converted to `not-null-col = ?` here, then the planner cannot do this
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// optimization and a table-full-scan will be generated.
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checker.cacheable = false
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checker.reason = "query has null constants"
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}
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checker.constCnt++
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if checker.constCnt > 50 { // just for safety and reduce memory cost
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checker.cacheable = false
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checker.reason = "query has more than 50 constants"
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}
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return in, !checker.cacheable
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case *ast.TableName:
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checker.tableNode = node
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if checker.schema != nil {
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tb, err := checker.schema.TableByName(node.Schema, node.Name)
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if err != nil {
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checker.cacheable = false
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checker.reason = "table cannot be found in schema"
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return in, !checker.cacheable
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}
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if tb.Meta().GetPartitionInfo() != nil {
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checker.cacheable = false
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checker.reason = "queries that access partitioning table are not supported"
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return in, !checker.cacheable
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}
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for _, col := range tb.Cols() {
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if col.IsGenerated() {
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checker.cacheable = false
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checker.reason = "queries that have generated columns are not supported"
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return in, !checker.cacheable
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}
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}
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if tb.Meta().TempTableType != model.TempTableNone {
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checker.cacheable = false
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checker.reason = "queries that access temporary tables are not supported"
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return in, !checker.cacheable
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}
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if tb.Meta().IsView() {
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checker.cacheable = false
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checker.reason = "queries that access views are not supported"
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return in, !checker.cacheable
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}
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if !tb.Type().IsNormalTable() {
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checker.cacheable = false
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checker.reason = "queries that access in-memory tables"
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return in, !checker.cacheable
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}
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}
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return in, !checker.cacheable
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}
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checker.cacheable = false // unexpected cases
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checker.reason = "query has some unsupported Node"
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return in, !checker.cacheable
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}
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// Leave implements Visitor interface.
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func (checker *nonPreparedPlanCacheableChecker) Leave(in ast.Node) (out ast.Node, ok bool) {
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if checker.isFilterNode(in) {
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checker.filterCnt--
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}
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return in, checker.cacheable
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}
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func (checker *nonPreparedPlanCacheableChecker) isFilterNode(node ast.Node) bool {
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switch node.(type) {
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case *ast.BetweenExpr, *ast.PatternInExpr, *ast.BinaryOperationExpr:
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return true
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}
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return false
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}
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func hasGeneratedCol(schema infoschema.InfoSchema, tn *ast.TableName) bool {
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tb, err := schema.TableByName(tn.Schema, tn.Name)
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if err != nil {
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logutil.BgLogger().Error("Error occur in checking cacheable", zap.Error(err))
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return false
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}
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for _, col := range tb.Cols() {
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if col.IsGenerated() {
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return true
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}
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}
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return false
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}
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func getColType(schema infoschema.InfoSchema, tbl *ast.TableName, col *ast.ColumnName) (colType byte, found bool) {
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if tbl == nil {
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return 0, false
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}
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tb, err := schema.TableByName(tbl.Schema, tbl.Name)
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if err != nil {
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return 0, false
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}
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for _, c := range tb.Cols() {
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if c.Name.L == col.Name.L {
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return c.GetType(), true
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}
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}
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return 0, false
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}
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func isTempTable(schema infoschema.InfoSchema, tn *ast.TableName) bool {
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tb, err := schema.TableByName(tn.Schema, tn.Name)
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if err != nil {
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logutil.BgLogger().Error("Error occur in checking cacheable", zap.Error(err))
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return false
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}
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if tb.Meta().TempTableType != model.TempTableNone {
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return true
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}
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return false
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}
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func isPartitionTable(schema infoschema.InfoSchema, tn *ast.TableName) bool {
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tb, err := schema.TableByName(tn.Schema, tn.Name)
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if err != nil {
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logutil.BgLogger().Error("Error occur in checking cacheable", zap.Error(err))
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return false
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}
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if tb.Meta().GetPartitionInfo() != nil {
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return true
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}
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return false
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}
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// isPlanCacheable returns whether this plan is cacheable and the reason if not.
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func isPlanCacheable(sctx sessionctx.Context, p Plan, paramNum, limitParamNum int) (cacheable bool, reason string) {
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var pp PhysicalPlan
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switch x := p.(type) {
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case *Insert:
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pp = x.SelectPlan
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case *Update:
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pp = x.SelectPlan
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case *Delete:
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pp = x.SelectPlan
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case PhysicalPlan:
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pp = x
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default:
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return false, fmt.Sprintf("skip plan-cache: unexpected un-cacheable plan %v", p.ExplainID().String())
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}
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if pp == nil { // simple DML statements
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return true, ""
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}
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if limitParamNum != 0 && !sctx.GetSessionVars().EnablePlanCacheForParamLimit {
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return false, "skip plan-cache: the switch 'tidb_enable_plan_cache_for_param_limit' is off"
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}
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return isPhysicalPlanCacheable(sctx, pp, paramNum, limitParamNum, false)
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}
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// isPhysicalPlanCacheable returns whether this physical plan is cacheable and return the reason if not.
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func isPhysicalPlanCacheable(sctx sessionctx.Context, p PhysicalPlan, paramNum, limitParamNum int, underIndexMerge bool) (cacheable bool, reason string) {
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var subPlans []PhysicalPlan
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switch x := p.(type) {
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case *PhysicalTableDual:
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if paramNum > 0 {
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return false, "skip plan-cache: get a TableDual plan"
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}
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case *PhysicalTableReader:
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if x.StoreType == kv.TiFlash {
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return false, "skip plan-cache: TiFlash plan is un-cacheable"
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}
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case *PhysicalShuffle, *PhysicalShuffleReceiverStub:
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return false, "skip plan-cache: get a Shuffle plan"
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case *PhysicalMemTable:
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return false, "skip plan-cache: PhysicalMemTable plan is un-cacheable"
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case *PhysicalIndexMergeReader:
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if x.AccessMVIndex {
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return false, "skip plan-cache: the plan with IndexMerge accessing Multi-Valued Index is un-cacheable"
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}
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underIndexMerge = true
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subPlans = append(subPlans, x.partialPlans...)
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case *PhysicalIndexScan:
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if underIndexMerge && x.isFullScan() {
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return false, "skip plan-cache: IndexMerge plan with full-scan is un-cacheable"
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}
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case *PhysicalTableScan:
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if underIndexMerge && x.isFullScan() {
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return false, "skip plan-cache: IndexMerge plan with full-scan is un-cacheable"
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}
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case *PhysicalApply:
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return false, "skip plan-cache: PhysicalApply plan is un-cacheable"
|
|
}
|
|
|
|
subPlans = append(subPlans, p.Children()...)
|
|
for _, c := range subPlans {
|
|
if cacheable, reason = isPhysicalPlanCacheable(sctx, c, paramNum, limitParamNum, underIndexMerge); !cacheable {
|
|
return cacheable, reason
|
|
}
|
|
}
|
|
return true, ""
|
|
}
|