Add support check for MAX_EXECUTION_TIME.

- This feature is request by [Feature 7008](pingcap#7008).
- Add support for system variable "session.max_execution_time" and "global.max_execution_time".
- Support hint in  Select Statement linke: "SELECT /*+ MAX_EXECUTION_TIME(1000) */ * FROM t1".
- Add some unit test for the above(all tests passed).

server/conn.go

@@ -1302,9 +1302,9 @@ func (cc *clientConn) writeChunks(ctx context.Context, rs ResultSet, binary bool
 		failpoint.Inject("SleepInwriteChunks", func(val failpoint.Value) {
 			time.Sleep(time.Duration(val.(int)) * time.Millisecond)
 		})
+		//MaxExecDuration() return 0 if there is no limit
 		if rs.MaxExecDuration().Nanoseconds() > 0 &&
 			time.Now().After(rs.StartExecTime().Add(rs.MaxExecDuration())) {
-			logutil.Logger(ctx).Warn("1907", zap.Int64("timeout:", rs.MaxExecDuration().Nanoseconds()))
 			return errors.New("Query execution was interrupted, max_execution_time exceeded")
 		}
 

server/conn_test.go

@@ -243,6 +243,16 @@ func (ts ConnTestSuite) TestConnExecutionTimeout(c *C) {
 	_, err = se.Execute(context.Background(), "select  * FROM tidb;")
 	c.Assert(err, IsNil)
 
+	_, err = se.Execute(context.Background(), "select  * FROM tidb;")
+	c.Assert(err, IsNil)
+
+	_, err = se.Execute(context.Background(), "set @@max_execution_time = 100;")
+	c.Assert(err, IsNil)
+
+	//session's max_execution_time has been set before
+	err = cc.handleQuery(context.Background(), "select  * FROM tidb;")
+	c.Assert(err.Error(), Equals, errors.New("Query execution was interrupted, max_execution_time exceeded").Error())
+
 	_, err = se.Execute(context.Background(), "set @@max_execution_time = 100;")
 	c.Assert(err, IsNil)
 

server/driver.go

@@ -141,8 +141,6 @@ type ResultSet interface {
 	StoreFetchedRows(rows []chunk.Row)
 	GetFetchedRows() []chunk.Row
 	Close() error
-	//	SetMaxExecDuration(time.Duration)
 	MaxExecDuration() time.Duration
-	//SetStartExecTime(time.Time)
 	StartExecTime() time.Time
 }

session/session.go

@@ -964,11 +964,10 @@ func (s *session) Execute(ctx context.Context, sql string) (recordSets []sqlexec
 }
 
 const (
-	// TiDBMaxExecutionTime is currently used for selection Statement only
-	TiDBMaxExecutionTime = "max_execution_time"
+	// MaxExecutionTime is currently used for selection Statement only
+	MaxExecutionTime = "max_execution_time"
 )
 
-//exeutionHints contains only maxExecutionTime now, but there maybe more in the future
 type exeutionHints struct {
 	maxExecutionTime uint64
 }
@@ -977,7 +976,7 @@ func (s *session) getExecutionHints(hints []*ast.TableOptimizerHint) (execHints
 	execHints = &exeutionHints{maxExecutionTime: 0}
 	for _, hint := range hints {
 		switch hint.HintName.L {
-		case TiDBMaxExecutionTime:
+		case MaxExecutionTime:
 			execHints.maxExecutionTime = hint.MaxExecutionTime
 		default:
 		}

session/session_test.go

@@ -2698,3 +2698,29 @@ func (s *testSessionSuite) TestGrantViewRelated(c *C) {
 	tkUser.MustQuery("select current_user();").Check(testkit.Rows("u_version29@%"))
 	tkUser.MustExec("create view v_version29_c as select * from v_version29;")
 }
+
+func (s *testSessionSuite) TestMaxExeucteTime(c *C) {
+	tk := testkit.NewTestKitWithInit(c, s.store)
+
+	tk.MustExec("create table MaxExecTime( id int,name varchar(128),age int);")
+	tk.MustExec("begin")
+	tk.MustExec("insert into MaxExecTime (id,name,age) values (1,'john',18),(2,'lary',19),(3,'lily',18);")
+
+	tk.MustQuery("select @@MAX_EXECUTION_TIME;").Check(testkit.Rows("0"))
+	tk.MustQuery("select @@global.MAX_EXECUTION_TIME;").Check(testkit.Rows("0"))
+	tk.MustQuery("select /*+ MAX_EXECUTION_TIME(1000) */ * FROM MaxExecTime;")
+
+	tk.MustExec("set @@global.MAX_EXECUTION_TIME = 300;")
+	tk.MustQuery("select * FROM MaxExecTime;")
+
+	tk.MustExec("set @@MAX_EXECUTION_TIME = 150;")
+	tk.MustQuery("select * FROM MaxExecTime;")
+
+	tk.MustQuery("select @@global.MAX_EXECUTION_TIME;").Check(testkit.Rows("300"))
+	tk.MustQuery("select @@MAX_EXECUTION_TIME;").Check(testkit.Rows("150"))
+
+	tk.MustExec("set @@global.MAX_EXECUTION_TIME = 0;")
+	tk.MustExec("set @@MAX_EXECUTION_TIME = 0;")
+	tk.MustExec("commit")
+	tk.MustExec("drop table if exists MaxExecTime;")
+}

sessionctx/variable/session.go

@@ -111,7 +111,7 @@ type TransactionContext struct {
 	TableDeltaMap map[int64]TableDelta
 	IsPessimistic bool
 
-	// For metrics.
+	// CreateTime For metrics.
 	CreateTime     time.Time
 	StatementCount int
 }
@@ -205,25 +205,24 @@ type SessionVars struct {
 	PreparedStmtNameToID map[string]uint32
 	// preparedStmtID is id of prepared statement.
 	preparedStmtID uint32
-	// params for prepared statements
+	// PreparedParams params for prepared statements
 	PreparedParams []types.Datum
 
 	// ActiveRoles stores active roles for current user
 	ActiveRoles []*auth.RoleIdentity
 
-	// retry information
 	RetryInfo *RetryInfo
-	// Should be reset on transaction finished.
+	//  TxnCtx Should be reset on transaction finished.
 	TxnCtx *TransactionContext
 
 	// KVVars is the variables for KV storage.
 	KVVars *kv.Variables
 
 	// TxnIsolationLevelOneShot is used to implements "set transaction isolation level ..."
 	TxnIsolationLevelOneShot struct {
-		// state 0 means default
-		// state 1 means it's set in current transaction.
-		// state 2 means it should be used in current transaction.
+		// State 0 means default
+		// State 1 means it's set in current transaction.
+		// State 2 means it should be used in current transaction.
 		State int
 		Value string
 	}
@@ -364,7 +363,7 @@ type SessionVars struct {
 	// CommandValue indicates which command current session is doing.
 	CommandValue uint32
 
-	// TIDBOptJoinOrderAlgoThreshold defines the minimal number of join nodes
+	// TiDBOptJoinReorderThreshold defines the minimal number of join nodes
 	// to use the greedy join reorder algorithm.
 	TiDBOptJoinReorderThreshold int
 
@@ -380,6 +379,8 @@ type SessionVars struct {
 	MaxExecutionTime uint64
 	// LowResolutionTSO is used for reading data with low resolution TSO which is updated once every two seconds.
 	LowResolutionTSO bool
+	// PessimisticLock indicates whether new transaction should be pessimistic .
+	PessimisticLock bool
 }
 
 // ConnectionInfo present connection used by audit.
@@ -690,7 +691,11 @@ func (s *SessionVars) SetSystemVar(name string, val string) error {
 			s.SetStatusFlag(mysql.ServerStatusInTrans, false)
 		}
 	case MaxExecutionTime:
-		s.MaxExecutionTime = uint64(tidbOptInt64(val, 0))
+		timeoutMS := tidbOptInt64(val, 0)
+		if timeoutMS < 0 {
+			timeoutMS = 0
+		}
+		s.MaxExecutionTime = uint64(timeoutMS)
 	case TiDBSkipUTF8Check:
 		s.SkipUTF8Check = TiDBOptOn(val)
 	case TiDBOptAggPushDown:
@@ -890,7 +895,7 @@ type Concurrency struct {
 	// HashAggPartialConcurrency is the number of concurrent hash aggregation partial worker.
 	HashAggPartialConcurrency int
 
-	// HashAggPartialConcurrency is the number of concurrent hash aggregation final worker.
+	// HashAggFinalConcurrency is the number of concurrent hash aggregation final worker.
 	HashAggFinalConcurrency int
 
 	// IndexSerialScanConcurrency is the number of concurrent index serial scan worker.