MySQL Packet for query is too large

Caused by: com.mysql.jdbc.PacketTooBigException: Packet for query is too large (3227 > 1024). You can change this value on the server by setting the max_allowed_packet' variable.
at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3178)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1917)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2060)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2536)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2465)
at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1383)
at sun.reflect.GeneratedMethodAccessor34.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.logicalcobwebs.proxool.ProxyStatement.invoke(ProxyStatement.java:100)
at org.logicalcobwebs.proxool.ProxyStatement.intercept(ProxyStatement.java:57)
at $java.sql.Statement
EnhancerByProxool
5159dcd0.executeQuery(<generated>)
at org.springframework.jdbc.core.JdbcTemplate$1QueryStatementCallback.doInStatement(JdbcTemplate.java:441)
at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:396)
... 52 more

原因： 查询出的数据包过大，默认情况下mysql 的字段容量不够装，所以抛出此异常

解决办法：

1.首先在控制台查询一下：SHOW VARIABLES LIKE '%max_allowed_packet%';

mysql> SHOW VARIABLES LIKE '%max_allowed_packet%';
+--------------------------+------------+
| Variable_name            | Value      |
+--------------------------+------------+
| max_allowed_packet       | 1024       |
| slave_max_allowed_packet | 1073741824 |
+--------------------------+------------+

默认情况下，最大允许数据包的容量是1M ,需要修改更大一点。20M

2.到mysql 的安装目录下找到 my.cnf 文件中，新增
[root@ecs-5d24-0001 ~]# vim /etc/my.cnf
[mysqld] 
character-set-server=utf8
max_allowed_packet=20M
 

备注：默认情况下是没有上述的标记，有就修改，没有就添加

3. 重启mysql服务

4.在控制台查看是否修改成功，在命令控制台输入：SHOW VARIABLES LIKE '%max_allowed_packet%';

显示：

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mysql> SHOW VARIABLES LIKE '%max_allowed_packet%';
+--------------------------+------------+
| Variable_name            | Value      |
+--------------------------+------------+
| max_allowed_packet       | 20971520   |
| slave_max_allowed_packet | 1073741824 |
+--------------------------+------------+
2 rows in set

5.修改成功，有效！

后续：

遇到mysql 服务停掉后，有时候设置的max_allowed_packed 的没有用，需要使用

set global max_allowed_packet = 2*1024*1024*10; 
设置成功了，以后重启也没事。