func (t *TxStructure) GetInt64(key []byte) (int64, error) {
	v, err := t.Get(key)
	if err != nil || v == nil {
		return 0, errors.Trace(err)
	}
	n, err := strconv.ParseInt(string(v), 10, 64)
	return n, errors.Trace(err)
}
GetInt64 gets the int64 value of a key.
package structure
import (
	"context"
	"strconv"
	"github.com/pingcap/errors"
	"github.com/pingcap/tidb/kv"
)
func (t *TxStructure) Set(key []byte, value []byte) error {
	if t.readWriter == nil {
		return errWriteOnSnapshot
	}
	ek := t.encodeStringDataKey(key)
	return t.readWriter.Set(ek, value)
}
func (t *TxStructure) Get(key []byte) ([]byte, error) {
	ek := t.encodeStringDataKey(key)
	value, err := t.reader.Get(context.TODO(), ek)
	if kv.ErrNotExist.Equal(err) {
		err = nil
	}
	return value, errors.Trace(err)
}