*: not send tso request when point get with max tso (#11981) (#16336)

executor/adapter.go

@@ -855,7 +855,7 @@ func (a *ExecStmt) SummaryStmt() {
 // IsPointGetWithPKOrUniqueKeyByAutoCommit returns true when meets following conditions:
 //  1. ctx is auto commit tagged
 //  2. txn is not valid
-//  2. plan is point get by pk, or point get by unique index (no double read)
+//  3. plan is point get by pk, or point get by unique index (no double read)
 func IsPointGetWithPKOrUniqueKeyByAutoCommit(ctx sessionctx.Context, p plannercore.Plan) (bool, error) {
 	// check auto commit
 	if !ctx.GetSessionVars().IsAutocommit() {

planner/optimize.go

@@ -15,6 +15,7 @@ package planner
 
 import (
 	"context"
+
 	"github.com/pingcap/parser/ast"
 	"github.com/pingcap/tidb/infoschema"
 	"github.com/pingcap/tidb/kv"
@@ -30,10 +31,15 @@ func Optimize(ctx context.Context, sctx sessionctx.Context, node ast.Node, is in
 	if _, containTiKV := sctx.GetSessionVars().GetIsolationReadEngines()[kv.TiKV]; containTiKV {
 		fp := plannercore.TryFastPlan(sctx, node)
 		if fp != nil {
+			if !isPointGetWithoutDoubleRead(sctx, fp) {
+				sctx.PrepareTxnFuture(ctx)
+			}
 			return fp, nil
 		}
 	}
 
+	sctx.PrepareTxnFuture(ctx)
+
 	// build logical plan
 	sctx.GetSessionVars().PlanID = 0
 	sctx.GetSessionVars().PlanColumnID = 0
@@ -79,6 +85,18 @@ func Optimize(ctx context.Context, sctx sessionctx.Context, node ast.Node, is in
 	return plannercore.DoOptimize(ctx, builder.GetOptFlag(), logic)
 }
 
+// isPointGetWithoutDoubleRead returns true when meets following conditions:
+//  1. ctx is auto commit tagged.
+//  2. plan is point get by pk.
+func isPointGetWithoutDoubleRead(ctx sessionctx.Context, p plannercore.Plan) bool {
+	if !ctx.GetSessionVars().IsAutocommit() {
+		return false
+	}
+
+	v, ok := p.(*plannercore.PointGetPlan)
+	return ok && v.IndexInfo == nil
+}
+
 func init() {
 	plannercore.OptimizeAstNode = Optimize
 }

session/session.go

@@ -1239,6 +1239,7 @@ func (s *session) PrepareStmt(sql string) (stmtID uint32, paramCount int, fields
 	// NewPrepareExec may need startTS to build the executor, for example prepare statement has subquery in int.
 	// So we have to call PrepareTxnCtx here.
 	s.PrepareTxnCtx(ctx)
+	s.PrepareTxnFuture(ctx)
 	prepareExec := executor.NewPrepareExec(s, executor.GetInfoSchema(s), sql)
 	err = prepareExec.Next(ctx, nil)
 	if err != nil {
@@ -1893,8 +1894,6 @@ func (s *session) PrepareTxnCtx(ctx context.Context) {
 		return
 	}
 
-	txnFuture := s.getTxnFuture(ctx)
-	s.txn.changeInvalidToPending(txnFuture)
 	is := domain.GetDomain(s).InfoSchema()
 	s.sessionVars.TxnCtx = &variable.TransactionContext{
 		InfoSchema:    is,
@@ -1911,6 +1910,16 @@ func (s *session) PrepareTxnCtx(ctx context.Context) {
 	}
 }
 
+// PrepareTxnFuture uses to try to get txn future.
+func (s *session) PrepareTxnFuture(ctx context.Context) {
+	if s.txn.validOrPending() {
+		return
+	}
+
+	txnFuture := s.getTxnFuture(ctx)
+	s.txn.changeInvalidToPending(txnFuture)
+}
+
 // RefreshTxnCtx implements context.RefreshTxnCtx interface.
 func (s *session) RefreshTxnCtx(ctx context.Context) error {
 	if err := s.doCommit(ctx); err != nil {

sessionctx/context.go

@@ -100,6 +100,8 @@ type Context interface {
 	ReleaseAllTableLocks()
 	// HasLockedTables uses to check whether this session locked any tables.
 	HasLockedTables() bool
+	// PrepareTxnFuture uses to prepare txn by future.
+	PrepareTxnFuture(ctx context.Context)
 }
 
 type basicCtxType int

util/mock/context.go

@@ -251,6 +251,10 @@ func (c *Context) HasLockedTables() bool {
 	return false
 }
 
+// PrepareTxnFuture implements the sessionctx.Context interface.
+func (c *Context) PrepareTxnFuture(ctx context.Context) {
+}
+
 // Close implements the sessionctx.Context interface.
 func (c *Context) Close() {
 }