From dffe29355a0b8a87f58ca13dd7304d97016faadf Mon Sep 17 00:00:00 2001
From: crazycs <crazycs520@gmail.com>
Date: Tue, 3 Sep 2019 23:11:49 +0800
Subject: [PATCH] *: not send tso request when point get with max tso (#11981)

---
 executor/adapter.go   |  2 +-
 planner/optimize.go   | 17 +++++++++++++++++
 session/session.go    | 13 +++++++++++--
 sessionctx/context.go |  2 ++
 util/mock/context.go  |  4 ++++
 5 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/executor/adapter.go b/executor/adapter.go
index 5c4fabb5b6..e79946e12c 100644
--- a/executor/adapter.go
+++ b/executor/adapter.go
@@ -769,7 +769,7 @@ func (a *ExecStmt) LogSlowQuery(txnTS uint64, succ bool) {
 // 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() {
diff --git a/planner/optimize.go b/planner/optimize.go
index b44ba76ff5..8ed38f5bb9 100644
--- a/planner/optimize.go
+++ b/planner/optimize.go
@@ -36,9 +36,14 @@ import (
 func Optimize(ctx context.Context, sctx sessionctx.Context, node ast.Node, is infoschema.InfoSchema) (plannercore.Plan, error) {
 	fp := plannercore.TryFastPlan(sctx, node)
 	if fp != nil {
+		if !isPointGetWithoutDoubleRead(sctx, fp) {
+			sctx.PrepareTxnFuture(ctx)
+		}
 		return fp, nil
 	}
 
+	sctx.PrepareTxnFuture(ctx)
+
 	var oriHint *bindinfo.HintsSet
 	if stmtNode, ok := node.(ast.StmtNode); ok {
 		oriHint = addHint(sctx, stmtNode)
@@ -203,6 +208,18 @@ func handleInvalidBindRecord(ctx context.Context, sctx sessionctx.Context, stmtN
 	}
 }
 
+// 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
 }
diff --git a/session/session.go b/session/session.go
index a801298f9a..d2f770c44f 100644
--- a/session/session.go
+++ b/session/session.go
@@ -1146,6 +1146,7 @@ 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 {
@@ -1785,8 +1786,6 @@ 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,
@@ -1807,6 +1806,16 @@ 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 {
diff --git a/sessionctx/context.go b/sessionctx/context.go
index 5589832918..97fd17948d 100644
--- a/sessionctx/context.go
+++ b/sessionctx/context.go
@@ -98,6 +98,8 @@ 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
diff --git a/util/mock/context.go b/util/mock/context.go
index 31ddddb5fe..889b5b2fd6 100644
--- a/util/mock/context.go
+++ b/util/mock/context.go
@@ -247,6 +247,10 @@ 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() {
 }