原因： （1）连接后没有关闭（2）死锁（3）程序重开的连接数太多等
解决 ：
（1）连接后如果不用及时关闭，
（2）手动关闭不用连接
mysql> show processlist;
+----+------+-----------+--------------------+---------+------+-------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+-----------+--------------------+---------+------+-------+------------------+
| 37 | root | localhost | information_schema | Query | 0 | NULL | show processlist |
| 38 | root | localhost | NULL | Sleep | 559 | | NULL |
+----+------+-----------+--------------------+---------+------+-------+------------------+
mysql> kill 40;
1 row in set (0.00 sec)
mysql> use information_schema
mysql> select id from processlist;
+----+
| id |
+----+
| 40 |
+----+
1 row in set (0.00 sec)
mysql> select concat('kill ',id,';') from information_schema.processlist where user='root' into outfile '/export/yoon.txt';
Query OK, 1 row affected (0.09 sec)
[root@db01 export]# more yoon.txt
kill 40;
批量删除会话：
mysql> source /export/yoon.txt
（3） 配置mysql最大连接数
这 种方式说来很简单，只要修改MySQL配置文件my.ini 或 my.cnf的参数max_connections，将其改为max_connections=1000，然后重启MySQL即可。
