*: add a variable tidb_slow_log_threshold to set the slow log threshold dynamically (#8094)

config/config.go

@@ -81,7 +81,7 @@ 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"`
 }
@@ -256,7 +256,7 @@ var defaultConf = Config{
 			LogRotate: true,
 			MaxSize:   logutil.DefaultLogMaxSize,
 		},
-		SlowThreshold:      300,
+		SlowThreshold:      logutil.DefaultSlowThreshold,
 		ExpensiveThreshold: 10000,
 		QueryLogMaxLen:     2048,
 	},

executor/adapter.go

@@ -17,6 +17,7 @@ import (
 	"fmt"
 	"math"
 	"strings"
+	"sync/atomic"
 	"time"
 
 	"github.com/juju/errors"
@@ -337,7 +338,7 @@ func (a *ExecStmt) LogSlowQuery(txnTS uint64, succ bool) {
 	}
 	cfg := config.GetGlobalConfig()
 	costTime := time.Since(a.StartTime)
-	threshold := time.Duration(cfg.Log.SlowThreshold) * time.Millisecond
+	threshold := time.Duration(atomic.LoadUint64(&cfg.Log.SlowThreshold)) * time.Millisecond
 	if costTime < threshold && level < log.DebugLevel {
 		return
 	}

executor/set_test.go

@@ -211,6 +211,13 @@ func (s *testSuite) TestSetVar(c *C) {
 	tk.MustQuery(`select @@session.sql_log_bin;`).Check(testkit.Rows("off"))
 	tk.MustExec("set @@sql_log_bin = on")
 	tk.MustQuery(`select @@session.sql_log_bin;`).Check(testkit.Rows("ON"))
+
+	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

@@ -28,6 +28,7 @@ import (
 	"github.com/pingcap/tidb/terror"
 	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tidb/util/auth"
+	"github.com/pingcap/tidb/util/logutil"
 )
 
 const (
@@ -567,6 +568,8 @@ 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 TiDBEnableStreaming:
 		s.EnableStreaming = TiDBOptOn(val)
 	case TiDBOptimizerSelectivityLevel:

sessionctx/variable/sysvar.go

@@ -20,6 +20,7 @@ import (
 	"github.com/pingcap/tidb/config"
 	"github.com/pingcap/tidb/mysql"
 	"github.com/pingcap/tidb/terror"
+	"github.com/pingcap/tidb/util/logutil"
 )
 
 // ScopeFlag is for system variable whether can be changed in global/session dynamically or not.
@@ -641,6 +642,7 @@ var defaultSysVars = []*SysVar{
 	{ScopeGlobal | ScopeSession, TiDBDisableTxnAutoRetry, boolToIntStr(DefTiDBDisableTxnAutoRetry)},
 	/* 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)},
 }

sessionctx/variable/tidb_vars.go

@@ -102,6 +102,9 @@ const (
 	// tidb_general_log is used to log every query in the server in info level.
 	TiDBGeneralLog = "tidb_general_log"
 
+	// tidb_slow_log_threshold is used to set the slow log threshold in the server.
+	TiDBSlowLogThreshold = "tidb_slow_log_threshold"
+
 	// tidb_enable_streaming enables TiDB to use streaming API for coprocessor requests.
 	TiDBEnableStreaming = "tidb_enable_streaming"
 

sessionctx/variable/varsutil.go

@@ -78,6 +78,8 @@ func GetSessionOnlySysVars(s *SessionVars, key string) (string, bool, error) {
 			return "", false, errors.Trace(err)
 		}
 		return string(j), true, nil
+	case TiDBSlowLogThreshold:
+		return strconv.FormatUint(atomic.LoadUint64(&config.GetGlobalConfig().Log.SlowThreshold), 10), true, nil
 	}
 	sVal, ok := s.systems[key]
 	if ok {

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.