planner: don't recompute the hashcode when generated column substitution doesn't happen (#46450)

Author: AilinKid

planner/core/BUILD.bazel

@@ -221,6 +221,7 @@ go_test(
         "planbuilder_test.go",
         "point_get_plan_test.go",
         "preprocess_test.go",
+        "rule_generate_column_substitute_test.go",
         "rule_join_reorder_dp_test.go",
         "rule_join_reorder_test.go",
         "rule_result_reorder_test.go",

planner/core/logical_plans_test.go

@@ -47,6 +47,26 @@ type plannerSuite struct {
 	ctx sessionctx.Context
 }
 
+func (p *plannerSuite) GetParser() *parser.Parser {
+	return p.p
+}
+
+func (p *plannerSuite) GetIS() infoschema.InfoSchema {
+	return p.is
+}
+
+func (p *plannerSuite) GetCtx() sessionctx.Context {
+	return p.ctx
+}
+
+func CreatePlannerSuite(sctx sessionctx.Context, is infoschema.InfoSchema) (s *plannerSuite) {
+	s = new(plannerSuite)
+	s.is = is
+	s.p = parser.New()
+	s.ctx = sctx
+	return s
+}
+
 func createPlannerSuite() (s *plannerSuite) {
 	s = new(plannerSuite)
 	tblInfos := []*model.TableInfo{

planner/core/rule_generate_column_substitute.go

@@ -76,12 +76,15 @@ func collectGenerateColumn(lp LogicalPlan, exprToColumn ExprColumnMap) {
 	}
 }
 
-func tryToSubstituteExpr(expr *expression.Expression, lp LogicalPlan, candidateExpr expression.Expression, tp types.EvalType, schema *expression.Schema, col *expression.Column, opt *logicalOptimizeOp) {
+func tryToSubstituteExpr(expr *expression.Expression, lp LogicalPlan, candidateExpr expression.Expression, tp types.EvalType, schema *expression.Schema, col *expression.Column, opt *logicalOptimizeOp) bool {
+	changed := false
 	if (*expr).Equal(lp.SCtx(), candidateExpr) && candidateExpr.GetType().EvalType() == tp &&
 		schema.ColumnIndex(col) != -1 {
 		*expr = col
 		appendSubstituteColumnStep(lp, candidateExpr, col, opt)
+		changed = true
 	}
+	return changed
 }
 
 func appendSubstituteColumnStep(lp LogicalPlan, candidateExpr expression.Expression, col *expression.Column, opt *logicalOptimizeOp) {
@@ -97,26 +100,38 @@ func appendSubstituteColumnStep(lp LogicalPlan, candidateExpr expression.Express
 	opt.appendStepToCurrent(lp.ID(), lp.TP(), reason, action)
 }
 
-func substituteExpression(cond expression.Expression, lp LogicalPlan, exprToColumn ExprColumnMap, schema *expression.Schema, opt *logicalOptimizeOp) {
+// SubstituteExpression is Exported for bench
+func SubstituteExpression(cond expression.Expression, lp LogicalPlan, exprToColumn ExprColumnMap, schema *expression.Schema, opt *logicalOptimizeOp) bool {
+	return substituteExpression(cond, lp, exprToColumn, schema, opt)
+}
+
+func substituteExpression(cond expression.Expression, lp LogicalPlan, exprToColumn ExprColumnMap, schema *expression.Schema, opt *logicalOptimizeOp) bool {
 	sf, ok := cond.(*expression.ScalarFunction)
 	if !ok {
-		return
+		return false
 	}
 	sctx := lp.SCtx().GetSessionVars().StmtCtx
+	changed := false
+	collectChanged := func(partial bool) {
+		if partial && !changed {
+			changed = true
+		}
+	}
 	defer func() {
 		// If the argument is not changed, hash code doesn't need to recount again.
-		// But we always do it to keep the code simple and stupid.
-		expression.ReHashCode(sf, sctx)
+		if changed {
+			expression.ReHashCode(sf, sctx)
+		}
 	}()
 	var expr *expression.Expression
 	var tp types.EvalType
 	switch sf.FuncName.L {
 	case ast.EQ, ast.LT, ast.LE, ast.GT, ast.GE:
 		for candidateExpr, column := range exprToColumn {
-			tryToSubstituteExpr(&sf.GetArgs()[1], lp, candidateExpr, sf.GetArgs()[0].GetType().EvalType(), schema, column, opt)
+			collectChanged(tryToSubstituteExpr(&sf.GetArgs()[1], lp, candidateExpr, sf.GetArgs()[0].GetType().EvalType(), schema, column, opt))
 		}
 		for candidateExpr, column := range exprToColumn {
-			tryToSubstituteExpr(&sf.GetArgs()[0], lp, candidateExpr, sf.GetArgs()[1].GetType().EvalType(), schema, column, opt)
+			collectChanged(tryToSubstituteExpr(&sf.GetArgs()[0], lp, candidateExpr, sf.GetArgs()[1].GetType().EvalType(), schema, column, opt))
 		}
 	case ast.In:
 		expr = &sf.GetArgs()[0]
@@ -132,21 +147,22 @@ func substituteExpression(cond expression.Expression, lp LogicalPlan, exprToColu
 		}
 		if canSubstitute {
 			for candidateExpr, column := range exprToColumn {
-				tryToSubstituteExpr(expr, lp, candidateExpr, tp, schema, column, opt)
+				collectChanged(tryToSubstituteExpr(expr, lp, candidateExpr, tp, schema, column, opt))
 			}
 		}
 	case ast.Like:
 		expr = &sf.GetArgs()[0]
 		tp = sf.GetArgs()[1].GetType().EvalType()
 		for candidateExpr, column := range exprToColumn {
-			tryToSubstituteExpr(expr, lp, candidateExpr, tp, schema, column, opt)
+			collectChanged(tryToSubstituteExpr(expr, lp, candidateExpr, tp, schema, column, opt))
 		}
 	case ast.LogicOr, ast.LogicAnd:
-		substituteExpression(sf.GetArgs()[0], lp, exprToColumn, schema, opt)
-		substituteExpression(sf.GetArgs()[1], lp, exprToColumn, schema, opt)
+		collectChanged(substituteExpression(sf.GetArgs()[0], lp, exprToColumn, schema, opt))
+		collectChanged(substituteExpression(sf.GetArgs()[1], lp, exprToColumn, schema, opt))
 	case ast.UnaryNot:
-		substituteExpression(sf.GetArgs()[0], lp, exprToColumn, schema, opt)
+		collectChanged(substituteExpression(sf.GetArgs()[0], lp, exprToColumn, schema, opt))
 	}
+	return changed
 }
 
 func (gc *gcSubstituter) substitute(ctx context.Context, lp LogicalPlan, exprToColumn ExprColumnMap, opt *logicalOptimizeOp) LogicalPlan {