gearman_mysql_udf安装成功，但调用不成功!

centos6.5下已经成功安装mysql5.6，gearman以及gearman_mysql_udf，也注册成功了udf函数，但在调用时，不能调用成功。

select gman_do_background('syncToRedis','fukai') as test;

+------+
| test |
+------+
| NULL |
+------+
1 row in set (0.00 sec)