func SetSessionSystemVar(vars *SessionVars, name string, value types.Datum) error {
	return nil
}
SetSessionSystemVar sets system variable and updates SessionVars states.
package variable
import (
	"strconv"
	"strings"
	"sync/atomic"
	"time"
	"github.com/pingcap/parser/mysql"
	"github.com/pingcap/tidb/types"
)
const secondsPerYear = 60 * 60 * 24 * 365
func SetDDLReorgWorkerCounter(cnt int32) {
	if cnt > maxDDLReorgWorkerCount {
		cnt = maxDDLReorgWorkerCount
	}
	atomic.StoreInt32(&ddlReorgWorkerCounter, cnt)
}
func GetDDLReorgWorkerCounter() int32 {
	return atomic.LoadInt32(&ddlReorgWorkerCounter)
}
func SetDDLReorgBatchSize(cnt int32) {
	if cnt > MaxDDLReorgBatchSize {
		cnt = MaxDDLReorgBatchSize
	}
	if cnt < MinDDLReorgBatchSize {
		cnt = MinDDLReorgBatchSize
	}
	atomic.StoreInt32(&ddlReorgBatchSize, cnt)
}
func GetDDLReorgBatchSize() int32 {
	return atomic.LoadInt32(&ddlReorgBatchSize)
}
func SetDDLErrorCountLimit(cnt int64) {
	atomic.StoreInt64(&ddlErrorCountlimit, cnt)
}
func GetDDLErrorCountLimit() int64 {
	return atomic.LoadInt64(&ddlErrorCountlimit)
}
func SetMaxDeltaSchemaCount(cnt int64) {
	atomic.StoreInt64(&maxDeltaSchemaCount, cnt)
}
func GetMaxDeltaSchemaCount() int64 {
	return atomic.LoadInt64(&maxDeltaSchemaCount)
}
func GetSessionSystemVar(s *SessionVars, key string) (string, error) {
	key = strings.ToLower(key)
	gVal, ok, err := GetSessionOnlySysVars(s, key)
	if err != nil || ok {
		return gVal, err
	}
	gVal, err = s.GlobalVarsAccessor.GetGlobalSysVar(key)
	if err != nil {
		return "", err
	}
	s.systems[key] = gVal
	return gVal, nil
}
func GetSessionOnlySysVars(s *SessionVars, key string) (string, bool, error) {
	return "", false, nil
}
func GetGlobalSystemVar(s *SessionVars, key string) (string, error) {
	key = strings.ToLower(key)
	gVal, ok, err := GetScopeNoneSystemVar(key)
	if err != nil || ok {
		return gVal, err
	}
	gVal, err = s.GlobalVarsAccessor.GetGlobalSysVar(key)
	if err != nil {
		return "", err
	}
	return gVal, nil
}
func GetScopeNoneSystemVar(key string) (string, bool, error) {
	return "", false, nil
}
const epochShiftBits = 18