摘要：
php$db=mysql_connect；var_转储（$db）；$db2=mysql_connect；var_转储；睡觉页面打印信息resourceoftyperesourceoftypemysql连接数mysql˃showfullprocesslist+-----+---------------+---------------+--------+---------------+------------+---------------+-|Id|用户|主机|数据库|命令|时间|状态|信息|+--------+--------+------------+--------+----------+|32 |根|localhost:54408|NULL |查询|0|NULL | showfullprocesslist||44|root|localhost:55278|NULL|Sleep|3||NULL |+---------------+---------------+------------+---------连接通过第四个参数后，重复调用它。
1、当 函数 mysql_connect 的前三个参数（serverusernamepassword）相同，mysql_connect 是会返回相同的连接。并且第四个参数（new_link）不传递时候，重复调用
php代码
<?php $db = mysql_connect('localhost','root','root'); var_dump($db); $db2 = mysql_connect('localhost','root','root'); var_dump($db2); sleep(10);
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 set2、当函数 mysql_connect 传递了第四个参数（new_link
php代码
<?php $db = mysql_connect('localhost','root','root',1); var_dump($db); $db2 = mysql_connect('localhost','root','root',1); var_dump($db2); sleep(10);
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
<?php $db = mysql_pconnect('localhost','root','root'); var_dump($db); $db2 = mysql_pconnect('localhost','root','root'); var_dump($db2);
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
<?php $db = mysql_pconnect('localhost','root','root',1); var_dump($db); $db2 = mysql_pconnect('localhost','root','root',1); var_dump($db2);
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 set5、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。