Mysql的max_allowed_packet设定

max_allowed_packet是Mysql中的一个设定参数，用于设定所接受的包的大小，根据情形不同，其缺省值可能是1M或者4M，比如是4M的情况下，这个值的大小即为：4 *1024*1024= 4194304

现象

当日志中出现了诸如：“Package for query is too large （xxxxxxxx > 4194304). You can change this value on the server by setting the max_allowed_package variable”的提示的时候，错误的本身就清楚的提示了对应的方式。

确认max_allowed_package

使用如下的方式可以确认当前设定值

  mysql> select @@max_allowed_packet;  +----------------------+  | @@max_allowed_packet |  +----------------------+  |       4194304 |  +----------------------+  1 row in set (0.00 sec)  mysql>

或者

  mysql> show variables like 'max_allowed_packet';  +--------------------+---------+  | Variable_name   | Value  |  +--------------------+---------+  | max_allowed_packet | 4194304 |  +--------------------+---------+  1 row in set (0.00 sec)  mysql>

修改

可以使用set命令来修改，但是只是临时修改，重启后即丢失。也可以直接修改过 mysql的设定文件并重启mysql服务，即可永久化保证设定。

根据mysql的安装不同修改的文件也会有所不同，普通安装方式可能会修改my.cnf，这里使用mysql的官方镜像，其修改的文件应该为：/etc/mysql/mysql.conf.d/mysqld.cnf

修改内容：向此文件中添加如下设定
max_allowed_packet = 256M

修改前

  [mysqld]  pid-file = /var/run/mysqld/mysqld.pid  socket = /var/run/mysqld/mysqld.sock  datadir = /var/lib/mysql  #log-error = /var/log/mysql/error.log  # By default we only accept connections from localhost  #bind-address = 127.0.0.1  # Disabling symbolic-links is recommended to prevent assorted security risks  symbolic-links=0

修改后

  [mysqld]  pid-file = /var/run/mysqld/mysqld.pid  socket = /var/run/mysqld/mysqld.sock  datadir = /var/lib/mysql  #log-error = /var/log/mysql/error.log  # By default we only accept connections from localhost  #bind-address = 127.0.0.1  # Disabling symbolic-links is recommended to prevent assorted security risks  symbolic-links=0  max_allowed_packet = 256M

重启容器并确认

  mysql> show variables like '%max_allowed_pack%';  +--------------------------+------------+  | Variable_name      | Value   |  +--------------------------+------------+  | max_allowed_packet    | 268435456 |  | slave_max_allowed_packet | 1073741824 |  +--------------------------+------------+  2 rows in set (0.01 sec)  mysql>

所以已经看到已经成功设定为256M(268435456)了

  liumiaocn:~ liumiao$ echo "256*1024*1024" |bc  268435456  liumiaocn:~ liumiao$