MySQL server has gone away的解决方法

因工作需要，需要导入一个200M左右的sql到user库

执行命令

mysql> use user
Database changed
mysql> source /tmp/user.sql

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导入的过程中出现MySQL server has gone away错误，数据导入失败。

错误信息如下：

ERROR 2006 (HY000): MySQL server has gone away
ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
Connection id:    11
Current database: user

ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
Connection id:    12
Current database: user

ERROR 2006 (HY000): MySQL server has gone away
ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
Connection id:    13
Current database: user

开始以为是超时导致，因此调大了 connect_timeout 和
wait_timeout 的值。

重新执行后问题依旧。

解决方法：

查看资料，发现了 max_allowed_packet 参数，

官方解释是适当增大 max_allowed_packet 参数可以使client端到server端传递大数据时，系统能够分配更多的扩展内存来处理。

查看mysql max_allowed_packet的值

mysql> show global variables like 'max_allowed_packet';
+--------------------+---------+
| Variable_name      | Value   |
+--------------------+---------+
| max_allowed_packet | 4194304 |
+--------------------+---------+

可以看到是4M，然后调大为256M(1024*1024*256)

mysql> set global max_allowed_packet=268435456;
Query OK, 0 rows affected (0.00 sec)

mysql> show global variables like 'max_allowed_packet';
+--------------------+-----------+
| Variable_name      | Value     |
+--------------------+-----------+
| max_allowed_packet | 268435456 |
+--------------------+-----------+
1 row in set (0.00 sec)

修改后执行导入，一切正常，解决问题。

注意：

使用set global命令修改 max_allowed_packet 的值，重启mysql后会失效，还原为默认值。

如果想重启后不还原，可以打开 my.cnf 文件，添加
max_allowed_packet = 256M 即可。

原文出处：http://blog.csdn.net/fdipzone/article/details/51974165#comments