MySQL too many connections error
参考资料：
http://dba.stackexchange.com/questions/1558/how-long-is-too-long-for-mysql-connections-to-sleep
http://stackoverflow.com/questions/19822558/how-to-set-max-connections-in-mysql-programmatically
http://blog.csdn.net/vip_linux/article/details/9209485
运行 python web 程序时时出现此错误
而且进 mysql shell 时也进不去，出现此错误
我们用这个命令查询到都有哪些连接：
show processlist
发现有 200 多个 sleep 进程
然后用SHOW VARIABLES LIKE "max_connections";查询到只有 214，所以会出现此错误
我们可以修改 mysql 的三个配置
- max_connections
- interactive_timeout
- wait_timetout
分别用下面两个命令可以查询到具体配置:
show global variables like '%timeout';
SHOW VARIABLES LIKE "max_connections";
然后我们可以在不重启 mysql 的情况下，修改这些配置：
mysql> SET GLOBAL max_connections = 2048;
Query OK, 0 rows affected (0.00 sec)
mysql> SET GLOBAL interactive_timeout = 7200;
Query OK, 0 rows affected (0.00 sec)
mysql> SET GLOBAL wait_timeout = 7200;
Query OK, 0 rows affected (0.00 sec)
MySQL server has gone away long byte
if size of data you want to save in mysql is too large, it will get this error.
you can query the current size in mysql shell:
show variables like '%max_allowed_packet%'
then change the max_allowed_packet in my.cnf and reatart mysql server.
```shell
[mysqld]
max_allowed_packet=64M
```
or set it in mysql shell:
```shell
mysql> set global max_allowed_packet=64*1024*1024;
```