mysql MySqlConnection判断mysql是否连接成功and查看连接数和状态等

MySqlConnection conn = new MySqlConnection(connstr) //新建一个MySqlConnection数据库连接

1、mysql> show status like '%connect%';

   Connections，试图连接到（不管是否成功）MySQL服务器的连接数。
   Max_used_connections，服务器启动后已经同时使用的连接的最大数量。
   Threads_connected，当前的连接数。

2、mysql> show variables like '%connect%';

   max_connections，最大连接数。

3、修改max_connections

   在配置文件（my.cnf或my.ini）在最下面，天加一句：
   max_connections=32000
   然后，用命令重启：/etc/init.d/mysqld restart
   虽然这里写的32000，实际MySQL服务器允许的最大连接数16384；
   添加了最大允许连接数，对系统消耗增加不大。

4、mysql> show processlist;
显示当前正在执行的MySQL连接。

 mysql> show status like '%connect%';
 +-----------------------------------------------+---------+
 | Variable_name                                 | Value   |
 +-----------------------------------------------+---------+
 | Aborted_connects                              | 45643   |
 | Connection_errors_accept                      | 0       |
 | Connection_errors_internal                    | 0       |
 | Connection_errors_max_connections             | 2275689 |
 | Connection_errors_peer_address                | 15      |
 | Connection_errors_select                      | 0       |
 | Connection_errors_tcpwrap                     | 0       |
 | Connections                                   | 145379  |
 | Max_used_connections                          | 152     |
 | Performance_schema_session_connect_attrs_lost | 0       |
 | Ssl_client_connects                           | 0       |
 | Ssl_connect_renegotiates                      | 0       |
 | Ssl_finished_connects                         | 0       |
 | Threads_connected                             | 7       |
 +-----------------------------------------------+---------+
 14 rows in set (0.00 sec)

 mysql> show variables like '%connect%';
 +-----------------------------------------------+-----------------+
 | Variable_name                                 | Value           |
 +-----------------------------------------------+-----------------+
 | character_set_connection                      | utf8            |
 | collation_connection                          | utf8_general_ci |
 | connect_timeout                               | 10              |
 | disconnect_on_expired_password                | ON              |
 | init_connect                                  |                 |
 | max_connect_errors                            | 100             |
 | max_connections                               | 151             |
 | max_user_connections                          | 0               |
 | performance_schema_session_connect_attrs_size | 512             |
 +-----------------------------------------------+-----------------+
 9 rows in set (0.00 sec)

 mysql> show processlist;
 +--------+------+-----------------+------+---------+------+-------+------------------+
 | Id     | User | Host            | db   | Command | Time | State | Info             |
 +--------+------+-----------------+------+---------+------+-------+------------------+
 | 145367 | root | localhost       | NULL | Query   |    0 | init  | show processlist |
 | 145373 | root | localhost:58275 | push | Sleep   |  179 |       | NULL             |
 | 145374 | root | localhost:58276 | push | Sleep   |  179 |       | NULL             |
 | 145375 | root | localhost:58278 | push | Sleep   |  179 |       | NULL             |
 | 145376 | root | localhost:58280 | push | Sleep   |    0 |       | NULL             |
 | 145377 | root | localhost:58279 | push | Sleep   |    2 |       | NULL             |
 | 145378 | root | localhost:58282 | push | Sleep   |    0 |       | NULL             |
 +--------+------+-----------------+------+---------+------+-------+------------------+
 7 rows in set (0.00 sec)