func (gvc *GlobalVariableCache) Update(rows []chunk.Row, fields []*ast.ResultField) {
	gvc.Lock()
	gvc.lastModify = time.Now()
	gvc.rows = rows
	gvc.fields = fields
	gvc.Unlock()
}
Update updates the global variable cache.
package domain
import (
	"sync"
	"time"
	"github.com/pingcap/tidb/parser/ast"
	"github.com/pingcap/tidb/util/chunk"
)
type GlobalVariableCache struct {
	sync.RWMutex
	lastModify time.Time
	rows       []chunk.Row
	fields     []*ast.ResultField
	disable bool
}
const globalVariableCacheExpiry time.Duration = 2 * time.Second