max_allowed_packet是Mysql中的一個設定引數，用於設定所接受的包的大小，根據情形不同，其預設值可能是1M或者4M，比如是4M的情況下，這個值的大小即為：4 *1024*1024= 4194304

現象

當日志中出現了諸如：“Package for query is too large （xxxxxxxx > 4194304). You can change this value on the server by setting the max_allowed_package variable”的提示的時候，錯誤的本身就清楚的提示了對應的方式。

確認max_allowed_package

使用如下的方式可以確認當前設定值

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命令來修改，但是隻是臨時修改，重啟後即丟失。也可以直接修改過 mysql的設定檔案並重啟mysql服務，即可永久化保證設定。 根據mysql的安裝不同修改的檔案也會有所不同，普通安裝方式可能會修改my.cnf，這裡使用mysql的官方映象，其修改的檔案應該為：/etc/mysql/mysql.conf.d/mysqld.cnf

修改內容：向此檔案中新增如下設定 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
 

修改後

[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

重啟容器並確認

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>

所以已經看到已經成功設定為256M(268435456)了

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