vi php.ini
...
# if use connection pool
# default value is false
# since V4.05
use_connection_pool = false
# connections whose the idle time exceeds this time will be closed
# unit: second
# default value is 3600
# since V4.05
connection_pool_max_idle_time = 3600
...
如果use_connection_pool = true
connection_pool_max_idle_time = 3600
这样连接池就会保持3600s时间，这样会导致连接无法释放
原文：http://www.cnblogs.com/zenghui940/p/5157664.html