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expression: a constraint propagate framework mainly for partition pru…
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,166 @@ | ||
| // Copyright 2018 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 expression | ||
|
|
||
| import ( | ||
| "bytes" | ||
|
|
||
| "github.com/pingcap/parser/mysql" | ||
| "github.com/pingcap/tidb/sessionctx" | ||
| "github.com/pingcap/tidb/types" | ||
| "github.com/pingcap/tidb/util/chunk" | ||
| log "github.com/sirupsen/logrus" | ||
| ) | ||
|
|
||
| // exprSet is a Set container for expressions, each expression in it is unique. | ||
| // `tombstone` is deleted mark, if tombstone[i] is true, data[i] is invalid. | ||
| // `index` use expr.HashCode() as key, to implement the unique property. | ||
| type exprSet struct { | ||
| data []Expression | ||
| tombstone []bool | ||
| exists map[string]struct{} | ||
| constfalse bool | ||
| } | ||
|
|
||
| func (s *exprSet) Append(e Expression) bool { | ||
| if _, ok := s.exists[string(e.HashCode(nil))]; ok { | ||
| return false | ||
| } | ||
|
|
||
| s.data = append(s.data, e) | ||
| s.tombstone = append(s.tombstone, false) | ||
| s.exists[string(e.HashCode(nil))] = struct{}{} | ||
| return true | ||
| } | ||
|
|
||
| // Slice returns the valid expressions in the exprSet, this function has side effect. | ||
| func (s *exprSet) Slice() []Expression { | ||
| if s.constfalse { | ||
| return []Expression{&Constant{ | ||
| Value: types.NewDatum(false), | ||
| RetType: types.NewFieldType(mysql.TypeTiny), | ||
| }} | ||
| } | ||
|
|
||
| idx := 0 | ||
| for i := 0; i < len(s.data); i++ { | ||
| if !s.tombstone[i] { | ||
| s.data[idx] = s.data[i] | ||
| idx++ | ||
| } | ||
| } | ||
| return s.data[:idx] | ||
| } | ||
|
|
||
| func (s *exprSet) SetConstFalse() { | ||
| s.constfalse = true | ||
| } | ||
|
|
||
| func newExprSet(conditions []Expression) *exprSet { | ||
| var exprs exprSet | ||
| exprs.data = make([]Expression, 0, len(conditions)) | ||
| exprs.tombstone = make([]bool, 0, len(conditions)) | ||
| exprs.exists = make(map[string]struct{}, len(conditions)) | ||
| for _, v := range conditions { | ||
| exprs.Append(v) | ||
| } | ||
| return &exprs | ||
| } | ||
|
|
||
| type pgSolver2 struct{} | ||
|
|
||
| // PropagateConstant propagate constant values of deterministic predicates in a condition. | ||
| func (s pgSolver2) PropagateConstant(ctx sessionctx.Context, conditions []Expression) []Expression { | ||
| exprs := newExprSet(conditions) | ||
| s.fixPoint(ctx, exprs) | ||
| return exprs.Slice() | ||
| } | ||
|
|
||
| // fixPoint is the core of the constant propagation algorithm. | ||
| // It will iterate the expression set over and over again, pick two expressions, | ||
| // apply one to another. | ||
| // If new conditions can be infered, they will be append into the expression set. | ||
| // Until no more conditions can be infered from the set, the algorithm finish. | ||
| func (s pgSolver2) fixPoint(ctx sessionctx.Context, exprs *exprSet) { | ||
| for { | ||
| saveLen := len(exprs.data) | ||
| iterOnce(ctx, exprs) | ||
| if saveLen == len(exprs.data) { | ||
| break | ||
| } | ||
| } | ||
| return | ||
| } | ||
|
|
||
| // iterOnce picks two expressions from the set, try to propagate new conditions from them. | ||
| func iterOnce(ctx sessionctx.Context, exprs *exprSet) { | ||
| for i := 0; i < len(exprs.data); i++ { | ||
| if exprs.tombstone[i] { | ||
| continue | ||
| } | ||
| for j := 0; j < len(exprs.data); j++ { | ||
| if exprs.tombstone[j] { | ||
| continue | ||
| } | ||
| if i == j { | ||
| continue | ||
| } | ||
| solve(ctx, i, j, exprs) | ||
| } | ||
| } | ||
| } | ||
|
|
||
| // solve uses exprs[i] exprs[j] to propagate new conditions. | ||
| func solve(ctx sessionctx.Context, i, j int, exprs *exprSet) { | ||
| for _, rule := range rules { | ||
| rule(ctx, i, j, exprs) | ||
| } | ||
| } | ||
|
|
||
| type constantPropagateRule func(ctx sessionctx.Context, i, j int, exprs *exprSet) | ||
|
|
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| var rules = []constantPropagateRule{ | ||
| ruleConstantFalse, | ||
| ruleColumnEQConst, | ||
| } | ||
|
|
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| // ruleConstantFalse propagates from CNF condition that false plus anything returns false. | ||
| // false, a = 1, b = c ... => false | ||
| func ruleConstantFalse(ctx sessionctx.Context, i, j int, exprs *exprSet) { | ||
| cond := exprs.data[i] | ||
| if cons, ok := cond.(*Constant); ok { | ||
| v, isNull, err := cons.EvalInt(ctx, chunk.Row{}) | ||
| if err != nil { | ||
| log.Error(err) | ||
| return | ||
| } | ||
| if !isNull && v == 0 { | ||
| exprs.SetConstFalse() | ||
| } | ||
| } | ||
| } | ||
|
|
||
| // ruleColumnEQConst propagates the "column = const" condition. | ||
| // "a = 3, b = a, c = a, d = b" => "a = 3, b = 3, c = 3, d = 3" | ||
| func ruleColumnEQConst(ctx sessionctx.Context, i, j int, exprs *exprSet) { | ||
| col, cons := validEqualCond(exprs.data[i]) | ||
| if col != nil { | ||
| expr := ColumnSubstitute(exprs.data[j], NewSchema(col), []Expression{cons}) | ||
| stmtctx := ctx.GetSessionVars().StmtCtx | ||
| if bytes.Compare(expr.HashCode(stmtctx), exprs.data[j].HashCode(stmtctx)) != 0 { | ||
| exprs.Append(expr) | ||
| exprs.tombstone[j] = true | ||
| } | ||
| } | ||
| } |