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