1、当 函数 mysql_connect 的前三个参数(server username password)相同，并且第四个参数(new_link)不传递时候，重复调用mysql_connect 是会返回相同的连接。

php代码

页面打印信息

resource(3) of type (mysql link) resource(3) of type (mysql link)

mysql连接数

mysql> show full processlist;

+----+------+-----------------+------+---------+------+-------+-----------------------+

| Id | User | Host | db | Command | Time | State | Info |

+----+------+-----------------+------+---------+------+-------+-----------------------+

| 32 | root | localhost:54408 | NULL | Query | 0 | NULL | show full processlist |

| 44 | root | localhost:55278 | NULL | Sleep | 3 | | NULL |

+----+------+-----------------+------+---------+------+-------+-----------------------+

2 rows in set

2、当函数 mysql_connect 传递了第四个参数(new_link)后，再重复调用它。

php代码

页面打印信息

resource(3) of type (mysql link) resource(5) of type (mysql link)

mysql连接数

mysql> show full processlist;

+----+------+-----------------+------+---------+------+-------+-----------------------+

| Id | User | Host | db | Command | Time | State | Info |

+----+------+-----------------+------+---------+------+-------+-----------------------+

| 32 | root | localhost:54408 | NULL | Query | 0 | NULL | show full processlist |

| 45 | root | localhost:55320 | NULL | Sleep | 4 | | NULL |

| 46 | root | localhost:55321 | NULL | Sleep | 4 | | NULL |

+----+------+-----------------+------+---------+------+-------+-----------------------+

3、mysql_pconnect 持久连接

php代码

页面打印信息

resource(3) of type (mysql link persistent) resource(4) of type (mysql link persistent)

mysql连接数

mysql> show full processlist;

+----+------+-----------------+------+---------+------+-------+-----------------------+

| Id | User | Host | db | Command | Time | State | Info |

+----+------+-----------------+------+---------+------+-------+-----------------------+

| 1 | root | localhost:55391 | NULL | Query | 0 | NULL | show full processlist |

| 2 | root | localhost:55393 | NULL | Sleep | 5 | | NULL |

+----+------+-----------------+------+---------+------+-------+-----------------------+

4、mysql_pconnect 加上第四个参数(new_link)即可 建立多个 持久连接

php代码

页面打印信息

resource(3) of type (mysql link persistent) resource(4) of type (mysql link persistent)

mysql连接数

mysql> show full processlist;

+----+------+-----------------+------+---------+------+-------+-----------------------+

| Id | User | Host | db | Command | Time | State | Info |

+----+------+-----------------+------+---------+------+-------+-----------------------+

| 1 | root | localhost:55391 | NULL | Query | 0 | NULL | show full processlist |

| 2 | root | localhost:55393 | NULL | Sleep | 316 | | NULL |

| 3 | root | localhost:55418 | NULL | Sleep | 4 | | NULL |

+----+------+-----------------+------+---------+------+-------+-----------------------+

3 rows in set

5、总结：

函数 mysql_pconnetc 创建的 持久化连接 在php脚本结束后，mysql的连接并不会立即结束。什么时候结束，是由mysql自己管理。函数 mysql_colse 不能关闭 mysql_pconnetc 的连接。

函数 mysql_connetc 创建的 连接 在php脚本结束后，mysql的连接也会相应结束。