memcache php 长连接

由于框架提供的memcachewrapper内部对memcache使用方法有误，导致长连接过多，（线上四台web机器每台有4000链接连在了两台memcache服务器上）

具体bug说明参见 https://bugs.php.net/bug.php?id=60460

引用

Memcache::addServer() does a *presistent* connection by default, if you do not
specify it to be different.

memcache::close() function doesn't close persistent connections, which are closed
only during web-server shutdown/restart.

so this is not a bug at all, but a coding error.

亦即问题是错误的使用Memcache::addServer所致。调用addserver时，如果设置persistent为true，则此链接将不会关闭，直至web server重启；即使显示调用close也没用。而php为短执行进程，执行完毕退出后新执行脚本又发起addServer的新链接，从而导致链接数不停增加。

使用Memcache::connect则不会出现此问题，其实也就是persistent=false的形式。

对应的还可以参考

引用

Memcache::pconnect()is similar to Memcache::connect() with the difference, that the connection it establishes is persistent. This connection is not closed after the end of script execution and by Memcache::close() function.

也是长连接