pkg/planner: build multiple logical plans from shared AST in optimize

pkg/planner/optimize.go

@@ -438,6 +438,95 @@ var planBuilderPool = sync.Pool{
 	},
 }
 
+type logicalPlanBuildCtx struct {
+	stmtCtxState             stmtctx.LogicalPlanBuildState
+	plannerSelectBlockAsName *[]ast.HintTable
+}
+
+func saveLogicalPlanBuildCtx(sessVars *variable.SessionVars) logicalPlanBuildCtx {
+	return logicalPlanBuildCtx{
+		stmtCtxState:             sessVars.StmtCtx.SaveLogicalPlanBuildState(),
+		plannerSelectBlockAsName: sessVars.PlannerSelectBlockAsName.Load(),
+	}
+}
+
+func restoreLogicalPlanBuildCtx(sessVars *variable.SessionVars, logicalPlanCtx logicalPlanBuildCtx) {
+	sessVars.StmtCtx.RestoreLogicalPlanBuildState(logicalPlanCtx.stmtCtxState)
+	sessVars.PlannerSelectBlockAsName.Store(logicalPlanCtx.plannerSelectBlockAsName)
+}
+
+func buildAndOptimizeLogicalPlanRound(
+	ctx context.Context,
+	sctx planctx.PlanContext,
+	node *resolve.NodeW,
+	is infoschema.InfoSchema,
+	hintProcessor *hint.QBHintHandler,
+	checked *bool,
+	needRestoreLogicalPlanCtx bool,
+	bestPlan *base.PhysicalPlan,
+	bestNames *types.NameSlice,
+	bestCost *float64,
+	bestLogicalPlanCtx *logicalPlanBuildCtx,
+) (base.Plan, types.NameSlice, bool, error) {
+	builder := planBuilderPool.Get().(*core.PlanBuilder)
+	defer planBuilderPool.Put(builder.ResetForReuse())
+
+	builder.Init(sctx, is, hintProcessor)
+
+	// todo: you can customize each round's special builder (like semi join rewrite or not by signal)
+	p, err := buildLogicalPlan(ctx, sctx, node, builder)
+	if err != nil {
+		return nil, nil, false, err
+	}
+	names := p.OutputNames()
+
+	if !*checked {
+		// Keep privilege and lock checks fail-fast. These depend on visitInfo
+		// produced by the logical build, but not on the later cost winner.
+		if pm := privilege.GetPrivilegeManager(sctx); pm != nil {
+			visitInfo := core.VisitInfo4PrivCheck(ctx, is, node.Node, builder.GetVisitInfo())
+			if err := core.CheckPrivilege(sctx.GetSessionVars().ActiveRoles, pm, visitInfo); err != nil {
+				return nil, nil, false, err
+			}
+		}
+
+		if err := core.CheckTableLock(sctx, is, builder.GetVisitInfo()); err != nil {
+			return nil, nil, false, err
+		}
+
+		if err := core.CheckTableMode(node); err != nil {
+			return nil, nil, false, err
+		}
+		*checked = true
+	}
+
+	// Handle the non-logical plan statement.
+	logic, isLogicalPlan := p.(base.LogicalPlan)
+	if !isLogicalPlan {
+		builder.HandleUnusedViewHints()
+		return p, names, true, nil
+	}
+
+	core.RecheckCTE(logic)
+
+	// todo: also you can customize each round's special logical opt flag here (like decorrelate rule or not)
+	finalPlan, cost, err := core.DoOptimize(ctx, sctx, builder.GetOptFlag(), logic)
+	if err != nil {
+		return nil, nil, false, err
+	}
+	builder.HandleUnusedViewHints()
+
+	if *bestPlan == nil || cost < *bestCost {
+		*bestCost = cost
+		*bestPlan = finalPlan
+		*bestNames = names
+		if needRestoreLogicalPlanCtx {
+			*bestLogicalPlanCtx = saveLogicalPlanBuildCtx(sctx.GetSessionVars())
+		}
+	}
+	return p, names, false, nil
+}
+
 // optimizeCnt is a global variable only used for test.
 var optimizeCnt int
 
@@ -457,53 +546,60 @@ func optimize(ctx context.Context, sctx planctx.PlanContext, node *resolve.NodeW
 	})
 	sessVars := sctx.GetSessionVars()
 
-	// build logical plan
+	// Build the logical plan from the raw AST. The hint processor only keeps
+	// AST-derived metadata; per-build state is allocated inside PlanBuilder.
 	hintProcessor := hint.NewQBHintHandler(sctx.GetSessionVars().StmtCtx)
 	node.Node.Accept(hintProcessor)
-	builder := planBuilderPool.Get().(*core.PlanBuilder)
-	defer planBuilderPool.Put(builder.ResetForReuse())
-	builder.Init(sctx, is, hintProcessor)
-	defer builder.HandleUnusedViewHints()
-	p, err := buildLogicalPlan(ctx, sctx, node, builder)
-	if err != nil {
-		return nil, nil, 0, err
+
+	// build multi logical plan from raw AST.
+	var (
+		buildRound                = 1
+		needRestoreLogicalPlanCtx = buildRound > 1
+		bestCost                  = math.MaxFloat64
+		bestPlan                  base.PhysicalPlan
+		bestNames                 types.NameSlice
+		bestLogicalPlanCtx        logicalPlanBuildCtx
+		checked                   bool
+	)
+	var initialLogicalPlanCtx logicalPlanBuildCtx
+	if needRestoreLogicalPlanCtx {
+		initialLogicalPlanCtx = saveLogicalPlanBuildCtx(sessVars)
 	}
+	beginOpt := time.Now()
+	for i := range buildRound {
+		if needRestoreLogicalPlanCtx && i > 0 {
+			restoreLogicalPlanBuildCtx(sessVars, initialLogicalPlanCtx)
+		}
 
-	activeRoles := sessVars.ActiveRoles
-	// Check privilege. Maybe it's better to move this to the Preprocess, but
-	// we need the table information to check privilege, which is collected
-	// into the visitInfo in the logical plan builder.
-	if pm := privilege.GetPrivilegeManager(sctx); pm != nil {
-		visitInfo := core.VisitInfo4PrivCheck(ctx, is, node.Node, builder.GetVisitInfo())
-		if err := core.CheckPrivilege(activeRoles, pm, visitInfo); err != nil {
+		p, names, nonLogical, err := buildAndOptimizeLogicalPlanRound(
+			ctx,
+			sctx,
+			node,
+			is,
+			hintProcessor,
+			&checked,
+			needRestoreLogicalPlanCtx,
+			&bestPlan,
+			&bestNames,
+			&bestCost,
+			&bestLogicalPlanCtx,
+		)
+		if err != nil {
 			return nil, nil, 0, err
 		}
+		if nonLogical {
+			// keep compatible with the old.
+			return p, names, 0, nil
+		}
 	}
-
-	if err := core.CheckTableLock(sctx, is, builder.GetVisitInfo()); err != nil {
-		return nil, nil, 0, err
-	}
-
-	if err := core.CheckTableMode(node); err != nil {
-		return nil, nil, 0, err
+	if bestPlan == nil {
+		return nil, nil, 0, errors.New("failed to build logical plan")
 	}
-
-	names := p.OutputNames()
-
-	// Handle the non-logical plan statement.
-	logic, isLogicalPlan := p.(base.LogicalPlan)
-	if !isLogicalPlan {
-		return p, names, 0, nil
+	if needRestoreLogicalPlanCtx {
+		restoreLogicalPlanBuildCtx(sessVars, bestLogicalPlanCtx)
 	}
-
-	core.RecheckCTE(logic)
-
-	beginOpt := time.Now()
-	finalPlan, cost, err := core.DoOptimize(ctx, sctx, builder.GetOptFlag(), logic)
-	// TODO: capture plan replayer here if it matches sql and plan digest
-
 	sessVars.DurationOptimizer.Total = time.Since(beginOpt)
-	return finalPlan, names, cost, err
+	return bestPlan, bestNames, bestCost, nil
 }
 
 // OptimizeExecStmt to handle the "execute" statement