mysql- Packet for query is too large (60 > -1).

mysqlamoebatomcat

连接池用tomcat jdbc ，数据库为mariadb10

中间经过amoeba代理读写分离

偶尔会报这个错

Caused by: com.mysql.jdbc.PacketTooBigException: Packet for query is too large (60 > -1). You can change this value on the server by setting the max_allowed_packet' variable.

mariadb SHOW VARIABLES LIKE 'max_allowed_packet';返回结果为
max_allowed_packet 67108864

不知道什么情况下会引起负值，请高手帮忙排查