Is it safe to keep database connections open for long time?

see http://stackoverflow.com/questions/312702/is-it-safe-to-keep-database-connections-open-for-long-time

其中的一个回复很有启发。如果不是这个功能要求7*24在运行的话，就没有必要保持长时间的数据库连接了。

If you are talking about a client/server application, I would recommend closing each connection as soon as you are done using it. While each individual application instance might take a small performance hit opening the connection, your application as a whole will scale better.