mysql报错Packet for query is too large (12238 > 1024). You can change this value

　　今天将项目部署到linux服务器的时候莫名其妙的报一些错误，可是在本地啥错没有，通过实时查看tomcat 的日志之后发现报错是:　　

实时查看日志:

1、先切换到：cd usr/local/tomcat5/logs

2、tail -f catalina.out

3、这样运行时就可以实时查看运行日志了

发现错误：

rg.springframework.dao.TransientDataAccessResourceException:
### Error querying database.  Cause: com.mysql.jdbc.PacketTooBigException: Packet for query is too large (1233 > 1024). You can change this value on the server by setting the max_allowed_packet' variable.
### The error may exist in cn/xm/exam/mapper/employee/out/custom/UnitCustomMapper.xml
### The error may involve cn.xm.exam.mapper.employee.out.custom.UnitCustomMapper.getHaulunitByCondition-Inline
### The error occurred while setting parameters
### SQL: SELECT   haulunit.unitId,   haulunit.unitBigId,   haulunit.bigId,   (select   group_concat(projectname) from project where projectid in (select projectId from   haulunitproject where bigId =haulunit.bigId and unitId=   haulunit.unitId)) as   projectNames,   haulunit.manager,   haulunit.managerPhone,   haulunit.secure,   haulunit.securePhone,   @b:=   (IFNULL((SELECT SUM(minusNum) FROM breakrules,   haulemployeeout WHERE   breakrules.BigEmployeeoutId =   haulemployeeout.BigEmployeeoutId    AND haulemployeeout.unitid =   haulunit.unitId           and breakTime LIKE CONCAT(Year(CurDate()),'%')   ),0)) AS unitMinisMum,   haulinfo.bigName,   haulinfo.bigStatus,   haulinfo.bigCreateDate,   unit.name,   unit.address,   unit.contact,   unit.phone,   @a:= (SELECT   COUNT(BigEmployeeoutId)   FROM haulemployeeout   WHERE   haulemployeeout.bigId   = haulunit.bigId   AND haulemployeeout.unitId =   haulunit.unitId and trainstatus='2') AS   personNum,   TRUNCATE(IFNULL(@b/@a,0),3) AS jiaquan   FROM haulunit,   haulinfo,   unit    WHERE haulunit.bigId=haulinfo.bigId AND    haulunit.unitId=unit.unitId                      and haulunit.bigId = ?     ORDER BY jiaquan desc               limit ?,?
### Cause: com.mysql.jdbc.PacketTooBigException: Packet for query is too large (1233 > 1024). You can change this value on the server by setting the max_allowed_packet' variable.
; SQL []; Packet for query is too large (1233 > 1024). You can change this value on the server by setting the max_allowed_packet' variable.; nested exception is com.mysql.jdbc.PacketTooBigException: Packet for query is too large (1233 > 1024). You can change this value on the server by setting the max_allowed_packet' variable.
        at org.springframework.jdbc.support.SQLStateSQLExceptionTranslator.doTranslate(SQLStateSQLExceptionTranslator.java:107)
        at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:72)
        at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:80)
        at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:80)

-----------------解决办法：(通过查看mysql全局变量发现原因是mysql限制了最大更新大小)----------------------

mysql max_allowed_packet 设置过小导致记录写入失败

mysql根据配置文件会限制server接受的数据包大小。

有时候大的插入和更新会受max_allowed_packet 参数限制，导致写入或者更新失败。

查看目前配置

show VARIABLES like '%max_allowed_packet%';

显示的结果为：

+--------------------+---------+

| Variable_name      | Value   |

+--------------------+---------+

| max_allowed_packet | 1048576 |

+--------------------+---------+  

以上说明目前的配置是：1M

修改方法

1、修改配置文件

可以编辑my.cnf来修改（windows下my.ini）,在[mysqld]段或者mysql的server配置段进行修改。

max_allowed_packet = 20M

如果找不到my.cnf可以通过

mysql --help | grep my.cnf

去寻找my.cnf文件。

linux下该文件在/etc/下。

2、在mysql命令行中修改

在mysql 命令行中运行

set global max_allowed_packet = 2*1024*1024*10

然后退出命令行，重启mysql服务，再进入。

show VARIABLES like '%max_allowed_packet%';

查看下max_allowed_packet是否编辑成功

 

 注意：该值设置过小将导致单个记录超过限制后写入数据库失败，且后续记录写入也将失败。

 

 

三、如何重启Linux的mysql

1、使用 service 启动：service mysqld restart

2、使用 mysqld 脚本启动：/etc/inint.d/mysqld restart