*: support AS OF TIMESTAMP read-only begin statement

executor/builder.go

@@ -706,10 +706,11 @@ func (b *executorBuilder) buildSimple(v *plannercore.Simple) Executor {
 	base := newBaseExecutor(b.ctx, v.Schema(), v.ID())
 	base.initCap = chunk.ZeroCapacity
 	e := &SimpleExec{
-		baseExecutor: base,
-		Statement:    v.Statement,
-		IsFromRemote: v.IsFromRemote,
-		is:           b.is,
+		baseExecutor:       base,
+		Statement:          v.Statement,
+		IsFromRemote:       v.IsFromRemote,
+		is:                 b.is,
+		StalenessTxnOption: v.StalenessTxnOption,
 	}
 	return e
 }

executor/simple.go

@@ -74,6 +74,9 @@ type SimpleExec struct {
 	IsFromRemote bool
 	done         bool
 	is           infoschema.InfoSchema
+
+	// StalenessTxnOption is used to execute the staleness txn during a read-only begin statement.
+	StalenessTxnOption *sessionctx.StalenessTxnOption
 }
 
 func (e *baseExecutor) getSysSession() (sessionctx.Context, error) {
@@ -566,13 +569,16 @@ func (e *SimpleExec) executeUse(s *ast.UseStmt) error {
 }
 
 func (e *SimpleExec) executeBegin(ctx context.Context, s *ast.BeginStmt) error {
-	// If `START TRANSACTION READ ONLY WITH TIMESTAMP BOUND` is the first statement in TxnCtx, we should
+	// If `START TRANSACTION READ ONLY` is the first statement in TxnCtx, we should
 	// always create a new Txn instead of reusing it.
 	if s.ReadOnly {
 		enableNoopFuncs := e.ctx.GetSessionVars().EnableNoopFuncs
-		if !enableNoopFuncs && s.Bound == nil {
+		if !enableNoopFuncs && s.AsOf == nil && s.Bound == nil {
 			return expression.ErrFunctionsNoopImpl.GenWithStackByArgs("READ ONLY")
 		}
+		if s.AsOf != nil {
+			return e.executeStartTransactionReadOnlyWithBoundedStaleness(ctx, s)
+		}
 		if s.Bound != nil {
 			return e.executeStartTransactionReadOnlyWithTimestampBound(ctx, s)
 		}
@@ -614,6 +620,22 @@ func (e *SimpleExec) executeBegin(ctx context.Context, s *ast.BeginStmt) error {
 	return nil
 }
 
+func (e *SimpleExec) executeStartTransactionReadOnlyWithBoundedStaleness(ctx context.Context, s *ast.BeginStmt) error {
+	if e.StalenessTxnOption == nil {
+		return errors.New("Failed to get timestamp during start transaction read only as of timestamp")
+	}
+	if err := e.ctx.NewTxnWithStalenessOption(ctx, *e.StalenessTxnOption); err != nil {
+		return err
+	}
+
+	// With START TRANSACTION, autocommit remains disabled until you end
+	// the transaction with COMMIT or ROLLBACK. The autocommit mode then
+	// reverts to its previous state.
+	e.ctx.GetSessionVars().SetInTxn(true)
+	return nil
+}
+
+// TODO: deprecate this syntax and only keep `AS OF TIMESTAMP` statement.
 func (e *SimpleExec) executeStartTransactionReadOnlyWithTimestampBound(ctx context.Context, s *ast.BeginStmt) error {
 	opt := sessionctx.StalenessTxnOption{}
 	opt.Mode = s.Bound.Mode
@@ -632,8 +654,7 @@ func (e *SimpleExec) executeStartTransactionReadOnlyWithTimestampBound(ctx conte
 		if err != nil {
 			return err
 		}
-		startTS := oracle.GoTimeToTS(gt)
-		opt.StartTS = startTS
+		opt.StartTS = oracle.GoTimeToTS(gt)
 	case ast.TimestampBoundExactStaleness:
 		// TODO: support funcCallExpr in future
 		v, ok := s.Bound.Timestamp.(*driver.ValueExpr)
@@ -668,8 +689,7 @@ func (e *SimpleExec) executeStartTransactionReadOnlyWithTimestampBound(ctx conte
 		if err != nil {
 			return err
 		}
-		startTS := oracle.GoTimeToTS(gt)
-		opt.StartTS = startTS
+		opt.StartTS = oracle.GoTimeToTS(gt)
 	}
 	err := e.ctx.NewTxnWithStalenessOption(ctx, opt)
 	if err != nil {

executor/stale_txn_test.go

@@ -73,13 +73,30 @@ func (s *testStaleTxnSerialSuite) TestExactStalenessTransaction(c *C) {
 			zone:        "sz",
 		},
 		{
-			name:        "begin",
+			name:        "begin after TimestampBoundReadTimestamp",
 			preSQL:      `START TRANSACTION READ ONLY WITH TIMESTAMP BOUND READ TIMESTAMP '2020-09-06 00:00:00';`,
 			sql:         "begin",
 			IsStaleness: false,
 			txnScope:    kv.GlobalTxnScope,
 			zone:        "",
 		},
+		{
+			name:             "AsOfTimestamp",
+			preSQL:           "begin",
+			sql:              `START TRANSACTION READ ONLY AS OF TIMESTAMP '2020-09-06 00:00:00';`,
+			IsStaleness:      true,
+			expectPhysicalTS: 1599321600000,
+			txnScope:         "local",
+			zone:             "sh",
+		},
+		{
+			name:        "begin after AsOfTimestamp",
+			preSQL:      `START TRANSACTION READ ONLY AS OF TIMESTAMP '2020-09-06 00:00:00';`,
+			sql:         "begin",
+			IsStaleness: false,
+			txnScope:    oracle.GlobalTxnScope,
+			zone:        "",
+		},
 	}
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test")
@@ -106,8 +123,8 @@ func (s *testStaleTxnSerialSuite) TestExactStalenessTransaction(c *C) {
 		}
 		c.Assert(tk.Se.GetSessionVars().TxnCtx.IsStaleness, Equals, testcase.IsStaleness)
 		tk.MustExec("commit")
-		failpoint.Disable("github.com/pingcap/tidb/config/injectTxnScope")
 	}
+	failpoint.Disable("github.com/pingcap/tidb/config/injectTxnScope")
 }
 
 func (s *testStaleTxnSerialSuite) TestStaleReadKVRequest(c *C) {
@@ -147,13 +164,17 @@ func (s *testStaleTxnSerialSuite) TestStaleReadKVRequest(c *C) {
 		failpoint.Enable("github.com/pingcap/tidb/config/injectTxnScope", fmt.Sprintf(`return("%v")`, testcase.zone))
 		failpoint.Enable("github.com/pingcap/tidb/store/tikv/assertStoreLabels", fmt.Sprintf(`return("%v_%v")`, placement.DCLabelKey, testcase.txnScope))
 		failpoint.Enable("github.com/pingcap/tidb/store/tikv/assertStaleReadFlag", `return(true)`)
+		// Using NOW() will cause the loss of fsp precision, so we use NOW(3) to be accurate to the millisecond.
+		tk.MustExec(`START TRANSACTION READ ONLY AS OF TIMESTAMP NOW(3);`)
+		tk.MustQuery(testcase.sql)
+		tk.MustExec(`commit`)
 		tk.MustExec(`START TRANSACTION READ ONLY WITH TIMESTAMP BOUND EXACT STALENESS '00:00:00';`)
 		tk.MustQuery(testcase.sql)
 		tk.MustExec(`commit`)
-		failpoint.Disable("github.com/pingcap/tidb/config/injectTxnScope")
-		failpoint.Disable("github.com/pingcap/tidb/store/tikv/assertStoreLabels")
-		failpoint.Disable("github.com/pingcap/tidb/store/tikv/assertStaleReadFlag")
 	}
+	failpoint.Disable("github.com/pingcap/tidb/config/injectTxnScope")
+	failpoint.Disable("github.com/pingcap/tidb/store/tikv/assertStoreLabels")
+	failpoint.Disable("github.com/pingcap/tidb/store/tikv/assertStaleReadFlag")
 }
 
 func (s *testStaleTxnSerialSuite) TestStalenessAndHistoryRead(c *C) {
@@ -169,6 +190,17 @@ func (s *testStaleTxnSerialSuite) TestStalenessAndHistoryRead(c *C) {
 	tk.MustExec(updateSafePoint)
 	// set @@tidb_snapshot before staleness txn
 	tk.MustExec(`set @@tidb_snapshot="2016-10-08 16:45:26";`)
+	tk.MustExec(`START TRANSACTION READ ONLY AS OF TIMESTAMP '2020-09-06 00:00:00';`)
+	// 1599321600000 == 2020-09-06 00:00:00
+	c.Assert(oracle.ExtractPhysical(tk.Se.GetSessionVars().TxnCtx.StartTS), Equals, int64(1599321600000))
+	tk.MustExec("commit")
+	// set @@tidb_snapshot during staleness txn
+	tk.MustExec(`START TRANSACTION READ ONLY AS OF TIMESTAMP '2020-09-06 00:00:00';`)
+	tk.MustExec(`set @@tidb_snapshot="2016-10-08 16:45:26";`)
+	c.Assert(oracle.ExtractPhysical(tk.Se.GetSessionVars().TxnCtx.StartTS), Equals, int64(1599321600000))
+	tk.MustExec("commit")
+	// set @@tidb_snapshot before staleness txn
+	tk.MustExec(`set @@tidb_snapshot="2016-10-08 16:45:26";`)
 	tk.MustExec(`START TRANSACTION READ ONLY WITH TIMESTAMP BOUND READ TIMESTAMP '2020-09-06 00:00:00';`)
 	c.Assert(oracle.ExtractPhysical(tk.Se.GetSessionVars().TxnCtx.StartTS), Equals, int64(1599321600000))
 	tk.MustExec("commit")
@@ -190,60 +222,76 @@ func (s *testStaleTxnSerialSuite) TestTimeBoundedStalenessTxn(c *C) {
 		name         string
 		sql          string
 		injectSafeTS uint64
-		useSafeTS    bool
+		// compareWithSafeTS will be 0 if StartTS==SafeTS, -1 if StartTS < SafeTS, and +1 if StartTS > SafeTS.
+		compareWithSafeTS int
 	}{
 		{
-			name: "max 20 seconds ago, safeTS 10 secs ago",
-			sql:  `START TRANSACTION READ ONLY WITH TIMESTAMP BOUND MAX STALENESS '00:00:20'`,
-			injectSafeTS: func() uint64 {
-				return oracle.GoTimeToTS(time.Now().Add(-10 * time.Second))
-			}(),
-			useSafeTS: true,
+			name:              "max 20 seconds ago, safeTS 10 secs ago",
+			sql:               `START TRANSACTION READ ONLY WITH TIMESTAMP BOUND MAX STALENESS '00:00:20'`,
+			injectSafeTS:      oracle.GoTimeToTS(time.Now().Add(-10 * time.Second)),
+			compareWithSafeTS: 0,
 		},
 		{
-			name: "max 10 seconds ago, safeTS 20 secs ago",
-			sql:  `START TRANSACTION READ ONLY WITH TIMESTAMP BOUND MAX STALENESS '00:00:10'`,
-			injectSafeTS: func() uint64 {
-				return oracle.GoTimeToTS(time.Now().Add(-20 * time.Second))
-			}(),
-			useSafeTS: false,
+			name:              "max 10 seconds ago, safeTS 20 secs ago",
+			sql:               `START TRANSACTION READ ONLY WITH TIMESTAMP BOUND MAX STALENESS '00:00:10'`,
+			injectSafeTS:      oracle.GoTimeToTS(time.Now().Add(-20 * time.Second)),
+			compareWithSafeTS: 1,
 		},
 		{
 			name: "max 20 seconds ago, safeTS 10 secs ago",
 			sql: func() string {
 				return fmt.Sprintf(`START TRANSACTION READ ONLY WITH TIMESTAMP BOUND MIN READ TIMESTAMP '%v'`,
 					time.Now().Add(-20*time.Second).Format("2006-01-02 15:04:05"))
 			}(),
-			injectSafeTS: func() uint64 {
-				return oracle.GoTimeToTS(time.Now().Add(-10 * time.Second))
-			}(),
-			useSafeTS: true,
+			injectSafeTS:      oracle.GoTimeToTS(time.Now().Add(-10 * time.Second)),
+			compareWithSafeTS: 0,
 		},
 		{
 			name: "max 10 seconds ago, safeTS 20 secs ago",
 			sql: func() string {
 				return fmt.Sprintf(`START TRANSACTION READ ONLY WITH TIMESTAMP BOUND MIN READ TIMESTAMP '%v'`,
 					time.Now().Add(-10*time.Second).Format("2006-01-02 15:04:05"))
 			}(),
-			injectSafeTS: func() uint64 {
-				return oracle.GoTimeToTS(time.Now().Add(-20 * time.Second))
-			}(),
-			useSafeTS: false,
+			injectSafeTS:      oracle.GoTimeToTS(time.Now().Add(-20 * time.Second)),
+			compareWithSafeTS: 1,
+		},
+		{
+			name:              "20 seconds ago to now, safeTS 10 secs ago",
+			sql:               `START TRANSACTION READ ONLY AS OF TIMESTAMP tidb_bounded_staleness(NOW() - INTERVAL 20 SECOND, NOW())`,
+			injectSafeTS:      oracle.GoTimeToTS(time.Now().Add(-10 * time.Second)),
+			compareWithSafeTS: 0,
+		},
+		{
+			name:              "10 seconds ago to now, safeTS 20 secs ago",
+			sql:               `START TRANSACTION READ ONLY AS OF TIMESTAMP tidb_bounded_staleness(NOW() - INTERVAL 10 SECOND, NOW())`,
+			injectSafeTS:      oracle.GoTimeToTS(time.Now().Add(-20 * time.Second)),
+			compareWithSafeTS: 1,
+		},
+		{
+			name:              "20 seconds ago to 10 seconds ago, safeTS 5 secs ago",
+			sql:               `START TRANSACTION READ ONLY AS OF TIMESTAMP tidb_bounded_staleness(NOW() - INTERVAL 20 SECOND, NOW() - INTERVAL 10 SECOND)`,
+			injectSafeTS:      oracle.GoTimeToTS(time.Now().Add(-5 * time.Second)),
+			compareWithSafeTS: -1,
 		},
 	}
 	for _, testcase := range testcases {
 		c.Log(testcase.name)
 		c.Assert(failpoint.Enable("github.com/pingcap/tidb/store/tikv/injectSafeTS",
 			fmt.Sprintf("return(%v)", testcase.injectSafeTS)), IsNil)
+		c.Assert(failpoint.Enable("github.com/pingcap/tidb/expression/injectSafeTS",
+			fmt.Sprintf("return(%v)", testcase.injectSafeTS)), IsNil)
 		tk.MustExec(testcase.sql)
-		if testcase.useSafeTS {
+		if testcase.compareWithSafeTS == 1 {
+			c.Assert(tk.Se.GetSessionVars().TxnCtx.StartTS, Greater, testcase.injectSafeTS)
+		} else if testcase.compareWithSafeTS == 0 {
 			c.Assert(tk.Se.GetSessionVars().TxnCtx.StartTS, Equals, testcase.injectSafeTS)
 		} else {
-			c.Assert(tk.Se.GetSessionVars().TxnCtx.StartTS, Greater, testcase.injectSafeTS)
+			c.Assert(tk.Se.GetSessionVars().TxnCtx.StartTS, Less, testcase.injectSafeTS)
 		}
 		tk.MustExec("commit")
-		failpoint.Disable("github.com/pingcap/tidb/store/tikv/injectSafeTS")
 	}
+	failpoint.Disable("github.com/pingcap/tidb/expression/injectSafeTS")
+	failpoint.Disable("github.com/pingcap/tidb/store/tikv/injectSafeTS")
 }
 
 func (s *testStaleTxnSerialSuite) TestStalenessTransactionSchemaVer(c *C) {
@@ -263,4 +311,16 @@ func (s *testStaleTxnSerialSuite) TestStalenessTransactionSchemaVer(c *C) {
 	schemaVer3 := tk.Se.GetSessionVars().GetInfoSchema().SchemaMetaVersion()
 	// got an old infoSchema
 	c.Assert(schemaVer3, Equals, schemaVer1)
+
+	schemaVer4 := tk.Se.GetSessionVars().GetInfoSchema().SchemaMetaVersion()
+	time.Sleep(time.Second)
+	tk.MustExec("create table t (id int primary key);")
+	schemaVer5 := tk.Se.GetSessionVars().GetInfoSchema().SchemaMetaVersion()
+	// confirm schema changed
+	c.Assert(schemaVer4, Less, schemaVer5)
+
+	tk.MustExec(`START TRANSACTION READ ONLY AS OF TIMESTAMP NOW() - INTERVAL 1 SECOND`)
+	schemaVer6 := tk.Se.GetSessionVars().GetInfoSchema().SchemaMetaVersion()
+	// got an old infoSchema
+	c.Assert(schemaVer6, Equals, schemaVer4)
 }

expression/builtin_time_test.go

@@ -2928,7 +2928,7 @@ func (s *testEvaluatorSuite) TestTiDBBoundedStaleness(c *C) {
 
 	// Test whether it's deterministic.
 	safeTime1 := t2.Add(-1 * time.Second)
-	safeTS1 := oracle.ComposeTS(safeTime1.Unix()*1000, 0)
+	safeTS1 := oracle.GoTimeToTS(safeTime1)
 	c.Assert(failpoint.Enable("github.com/pingcap/tidb/expression/injectSafeTS",
 		fmt.Sprintf("return(%v)", safeTS1)), IsNil)
 	f, err := fc.getFunction(s.ctx, s.datumsToConstants([]types.Datum{types.NewDatum(t1Str), types.NewDatum(t2Str)}))
@@ -2941,7 +2941,7 @@ func (s *testEvaluatorSuite) TestTiDBBoundedStaleness(c *C) {
 	c.Assert(resultTime, Equals, safeTime1.Format(types.TimeFormat))
 	// SafeTS updated.
 	safeTime2 := t2.Add(1 * time.Second)
-	safeTS2 := oracle.ComposeTS(safeTime2.Unix()*1000, 0)
+	safeTS2 := oracle.GoTimeToTS(safeTime2)
 	c.Assert(failpoint.Enable("github.com/pingcap/tidb/expression/injectSafeTS",
 		fmt.Sprintf("return(%v)", safeTS2)), IsNil)
 	f, err = fc.getFunction(s.ctx, s.datumsToConstants([]types.Datum{types.NewDatum(t1Str), types.NewDatum(t2Str)}))

planner/core/common_plans.go

@@ -723,6 +723,9 @@ type Simple struct {
 	//   and executing in co-processor.
 	//   Used for `global kill`. See https://github.com/pingcap/tidb/blob/master/docs/design/2020-06-01-global-kill.md.
 	IsFromRemote bool
+
+	// StalenessTxnOption is the transaction option that will be built when planner builder calls buildSimple.
+	StalenessTxnOption *sessionctx.StalenessTxnOption
 }
 
 // PhysicalSimpleWrapper is a wrapper of `Simple` to implement physical plan interface.

planner/core/planbuilder.go

@@ -43,6 +43,7 @@ import (
 	"github.com/pingcap/tidb/sessionctx/variable"
 	"github.com/pingcap/tidb/statistics"
 	"github.com/pingcap/tidb/store/tikv"
+	"github.com/pingcap/tidb/store/tikv/oracle"
 	"github.com/pingcap/tidb/table"
 	"github.com/pingcap/tidb/types"
 	driver "github.com/pingcap/tidb/types/parser_driver"
@@ -643,7 +644,7 @@ func (b *PlanBuilder) Build(ctx context.Context, node ast.Node) (Plan, error) {
 		*ast.GrantStmt, *ast.DropUserStmt, *ast.AlterUserStmt, *ast.RevokeStmt, *ast.KillStmt, *ast.DropStatsStmt,
 		*ast.GrantRoleStmt, *ast.RevokeRoleStmt, *ast.SetRoleStmt, *ast.SetDefaultRoleStmt, *ast.ShutdownStmt,
 		*ast.RenameUserStmt:
-		return b.buildSimple(node.(ast.StmtNode))
+		return b.buildSimple(ctx, node.(ast.StmtNode))
 	case ast.DDLNode:
 		return b.buildDDL(ctx, x)
 	case *ast.CreateBindingStmt:
@@ -2259,7 +2260,7 @@ func (b *PlanBuilder) buildShow(ctx context.Context, show *ast.ShowStmt) (Plan,
 	return np, nil
 }
 
-func (b *PlanBuilder) buildSimple(node ast.StmtNode) (Plan, error) {
+func (b *PlanBuilder) buildSimple(ctx context.Context, node ast.StmtNode) (Plan, error) {
 	p := &Simple{Statement: node}
 
 	switch raw := node.(type) {
@@ -2325,10 +2326,41 @@ func (b *PlanBuilder) buildSimple(node ast.StmtNode) (Plan, error) {
 		}
 	case *ast.ShutdownStmt:
 		b.visitInfo = appendVisitInfo(b.visitInfo, mysql.ShutdownPriv, "", "", "", nil)
+	case *ast.BeginStmt:
+		if raw.AsOf != nil {
+			startTS, err := b.calculateTsExpr(raw.AsOf)
+			if err != nil {
+				return nil, err
+			}
+			p.StalenessTxnOption = &sessionctx.StalenessTxnOption{
+				Mode:    ast.TimestampBoundReadTimestamp,
+				StartTS: startTS,
+			}
+		}
 	}
 	return p, nil
 }
 
+// calculateTsExpr calculates the TsExpr of AsOfClause to get a StartTS.
+func (b *PlanBuilder) calculateTsExpr(asOfClause *ast.AsOfClause) (uint64, error) {
+	tsVal, err := evalAstExpr(b.ctx, asOfClause.TsExpr)
+	if err != nil {
+		return 0, err
+	}
+	toTypeTimestamp := types.NewFieldType(mysql.TypeTimestamp)
+	// We need at least the millionsecond here, so set fsp to 3.
+	toTypeTimestamp.Decimal = 3
+	tsTimestamp, err := tsVal.ConvertTo(b.ctx.GetSessionVars().StmtCtx, toTypeTimestamp)
+	if err != nil {
+		return 0, err
+	}
+	tsTime, err := tsTimestamp.GetMysqlTime().GoTime(b.ctx.GetSessionVars().TimeZone)
+	if err != nil {
+		return 0, err
+	}
+	return oracle.GoTimeToTS(tsTime), nil
+}
+
 func collectVisitInfoFromRevokeStmt(sctx sessionctx.Context, vi []visitInfo, stmt *ast.RevokeStmt) []visitInfo {
 	// To use REVOKE, you must have the GRANT OPTION privilege,
 	// and you must have the privileges that you are granting.