*: add a variable tidb_slow_log_threshold to set the slow log threshold dynamically

config/config.go

@@ -88,7 +88,7 @@ type Log struct {
 	File logutil.FileLogConfig `toml:"file" json:"file"`
 
 	SlowQueryFile      string `toml:"slow-query-file" json:"slow-query-file"`
-	SlowThreshold      uint   `toml:"slow-threshold" json:"slow-threshold"`
+	SlowThreshold      uint64 `toml:"slow-threshold" json:"slow-threshold"`
 	ExpensiveThreshold uint   `toml:"expensive-threshold" json:"expensive-threshold"`
 	QueryLogMaxLen     uint   `toml:"query-log-max-len" json:"query-log-max-len"`
 }
@@ -275,7 +275,7 @@ var defaultConf = Config{
 			LogRotate: true,
 			MaxSize:   logutil.DefaultLogMaxSize,
 		},
-		SlowThreshold:      300,
+		SlowThreshold:      logutil.DefaultSlowThreshold,
 		ExpensiveThreshold: 10000,
 		QueryLogMaxLen:     2048,
 	},

executor/set_test.go

@@ -239,6 +239,13 @@ func (s *testSuite) TestSetVar(c *C) {
 	tk.MustQuery(`select @@session.tidb_constraint_check_in_place;`).Check(testkit.Rows("1"))
 	tk.MustExec("set global tidb_constraint_check_in_place = 0")
 	tk.MustQuery(`select @@global.tidb_constraint_check_in_place;`).Check(testkit.Rows("0"))
+
+	tk.MustExec("set tidb_slow_log_threshold = 0")
+	tk.MustQuery("select @@session.tidb_slow_log_threshold;").Check(testkit.Rows("0"))
+	tk.MustExec("set tidb_slow_log_threshold = 1")
+	tk.MustQuery("select @@session.tidb_slow_log_threshold;").Check(testkit.Rows("1"))
+	_, err = tk.Exec("set global tidb_slow_log_threshold = 0")
+	c.Assert(err, NotNil)
 }
 
 func (s *testSuite) TestSetCharset(c *C) {

sessionctx/variable/session.go

@@ -33,6 +33,7 @@ import (
 	"github.com/pingcap/tidb/sessionctx/stmtctx"
 	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tidb/util/chunk"
+	"github.com/pingcap/tidb/util/logutil"
 	"github.com/pingcap/tidb/util/timeutil"
 	"github.com/pkg/errors"
 )
@@ -607,6 +608,8 @@ func (s *SessionVars) SetSystemVar(name string, val string) error {
 		s.MemQuotaNestedLoopApply = tidbOptInt64(val, DefTiDBMemQuotaNestedLoopApply)
 	case TiDBGeneralLog:
 		atomic.StoreUint32(&ProcessGeneralLog, uint32(tidbOptPositiveInt32(val, DefTiDBGeneralLog)))
+	case TiDBSlowLogThreshold:
+		atomic.StoreUint64(&config.GetGlobalConfig().Log.SlowThreshold, uint64(tidbOptInt64(val, logutil.DefaultSlowThreshold)))
 	case TiDBRetryLimit:
 		s.RetryLimit = tidbOptInt64(val, DefTiDBRetryLimit)
 	case TiDBDisableTxnAutoRetry:

sessionctx/variable/sysvar.go

@@ -22,6 +22,7 @@ import (
 	"github.com/pingcap/parser/terror"
 	"github.com/pingcap/tidb/config"
 	"github.com/pingcap/tidb/kv"
+	"github.com/pingcap/tidb/util/logutil"
 )
 
 // ScopeFlag is for system variable whether can be changed in global/session dynamically or not.
@@ -662,6 +663,7 @@ var defaultSysVars = []*SysVar{
 	{ScopeSession, TiDBOptimizerSelectivityLevel, strconv.Itoa(DefTiDBOptimizerSelectivityLevel)},
 	/* The following variable is defined as session scope but is actually server scope. */
 	{ScopeSession, TiDBGeneralLog, strconv.Itoa(DefTiDBGeneralLog)},
+	{ScopeSession, TiDBSlowLogThreshold, strconv.Itoa(logutil.DefaultSlowThreshold)},
 	{ScopeSession, TiDBConfig, ""},
 	{ScopeGlobal | ScopeSession, TiDBDDLReorgWorkerCount, strconv.Itoa(DefTiDBDDLReorgWorkerCount)},
 	{ScopeSession, TiDBDDLReorgPriority, "PRIORITY_LOW"},

sessionctx/variable/tidb_vars.go

@@ -95,7 +95,10 @@ const (
 	// tidb_general_log is used to log every query in the server in info level.
 	TiDBGeneralLog = "tidb_general_log"
 
-	// tidb_retry_limit is the maximun number of retries when committing a transaction.
+	// tidb_slow_log_threshold is used to set the slow log threshold in the server.
+	TiDBSlowLogThreshold = "tidb_slow_log_threshold"
+
+	// tidb_retry_limit is the maximum number of retries when committing a transaction.
 	TiDBRetryLimit = "tidb_retry_limit"
 
 	// tidb_disable_txn_auto_retry disables transaction auto retry.

sessionctx/variable/varsutil.go

@@ -85,6 +85,8 @@ func GetSessionOnlySysVars(s *SessionVars, key string) (string, bool, error) {
 		return string(j), true, nil
 	case TiDBForcePriority:
 		return mysql.Priority2Str[mysql.PriorityEnum(atomic.LoadInt32(&ForcePriority))], true, nil
+	case TiDBSlowLogThreshold:
+		return strconv.FormatUint(atomic.LoadUint64(&config.GetGlobalConfig().Log.SlowThreshold), 10), true, nil
 	}
 	sVal, ok := s.systems[key]
 	if ok {
@@ -322,7 +324,7 @@ func ValidateSetSystemVar(vars *SessionVars, name string, value string) (string,
 		TIDBMemQuotaIndexLookupReader,
 		TIDBMemQuotaIndexLookupJoin,
 		TIDBMemQuotaNestedLoopApply,
-		TiDBRetryLimit:
+		TiDBRetryLimit, TiDBSlowLogThreshold:
 		_, err := strconv.ParseInt(value, 10, 64)
 		if err != nil {
 			return value, ErrWrongValueForVar.GenWithStackByArgs(name)

util/logutil/log.go

@@ -33,6 +33,8 @@ const (
 	DefaultLogMaxSize = 300 // MB
 	defaultLogFormat  = "text"
 	defaultLogLevel   = log.InfoLevel
+	// DefaultSlowThreshold is the default slow log threshold in millisecond.
+	DefaultSlowThreshold = 300
 )
 
 // FileLogConfig serializes file log related config in toml/json.