PHP Mysql数据库 长链接 短链接 （连接池 ？）

警告
PHP 5.5.0中不推荐使用此扩展，它在PHP 7.0.0中被删除。相反，应该使用MySQLi或PDO_MySQL扩展。另请参见MySQL：选择API指南和 相关常见问题以获取更多信息。此功能的替代方法包括：
mysqli_connect（）与 p：主机前缀
PDO :: __结构（）与PDO::ATTR_PERSISTENT作为驱动程序选项

mysql_pconnect and connection pooling are two different things. There are many problems connected with mysql_pconnect and first you should read the manual and carefully use it, but this is not connection pooling.
Connection pooling is a technique where the application server manages the connections. When the application needs a connection it asks the application server for it and the application server returns one of the pooled connections if there is one free.
We can do connection scaling in php for that please go through following link:oracle white php part
So no connection pooling in php.
As Julio said apache releases all resources when the request ends for the current reques. You can use mysql_pconnect but you are limited with that function and you must be very careful. Other choice is to use singleton pattern, but none of this is pooling.

Copyright 1997-2014 the PHP Documentation Group.
The plugins connection pool is created when PHP initializes its modules (MINIT) and free’d when PHP shuts down the modules (MSHUTDOWN). This is the same as for persistent MySQL connections.
Depending on the deployment model, the pool is used for the duration of one or multiple web requests. Network connections are bound to the lifespan of an operating system level process. If the PHP process serves multiple web requests as it is the case for Fast-CGI or threaded web server deployments, then the pooled connections can be reused over multiple connections. Because multiplexing means sharing connections, it can even happen with a threaded deployment that two threads or two distinct web requests are linked to one pooled network connections.
A pooled connection is explicitly closed once the last reference to it is released. An implicit close happens when PHP shuts down its modules.

版权所有1997-2014 PHP文档组。
当PHP初始化其modules（MINIT）时，插件连接池是创建的，当PHP关闭modules（）时，它们将被释放MSHUTDOWN。这与持久MySQL连接相同。
根据部署模式，池将用于一个或多个Web请求的持续时间。网络连接必须与操作系统级别进程的使用寿命相关联。如果PHP进程服务多个Web请求，就像Fast-CGI或线程Web服务器部署一样，则可以通过多个连接重用池连接。由于多路复用意味着共享连接，所以甚至可以通过线程部署来实现两个线程或两个不同的Web请求链接到一个池网络连接。
一旦释放了最后一次引用，就会显式关闭一个池化的连接。当PHP关闭其模块时，会发生隐式关闭。

里面提到连接池的是这个工具Mysqlnd 主从复制和负载均衡插件 （Mysqlnd replication and load balancing plugin ¶）
中的连接池与切换 ¶下面有这么句话

插件控制 PHP MySQL 链接，完成同步和负载均衡，他并不会改变现有的 PHP MySQL 扩展的方法使用 (mysqli, mysql, 和 PDO_MYSQL) 现有的应用并不需要 更新他们代码，或者使用新的 API，但是若操作行为改变，还是需要一些修改的。
插件结果下面这些扩展对于 MySQL 连接的控制， mysqli, mysql, 和 PDO_MYSQL。 并且为 mysqli, mysql, 和 PDO_MYSQL 提供一个本地的连接池 完成 MySQL 主从同步的 master 和 slave 通讯控制。插件会代理所有的 到达 master 和 slave 的查询请求。 在某一时刻一个连接到 master 的链接，会在稍后变更为 slave 连接，或者 依然保持 master 连接。在执行非事务处理中，控制和替换 PHP MySQL 的网络链接