我在许多网络语言中看到的一个常见问题是，数据库连接需要关闭，否则总连接数会逐渐增加，然后以任何形式停止。
HTTP是无状态的，当请求完成处理时，为什么这些语言不能丢弃请求打开的任何连接？有什么正当理由可以让它继续开放吗？
因为打开、验证和授权访问数据库的成本相当昂贵。这就是为什么通常每个人都使用数据库连接池的原因。当请求处理程序从池中提取可用的已打开连接时，连接仍处于打开状态。当一个人关闭一个连接时，真正发生的事情是该连接被释放给其他人使用。
要回答。。。
why can t these languages just drop any connections that request opened? Are there any legitimate reasons for why you might keep it open?
请求完成后，连接可能会保持打开状态，并用于其他目的。例如，数据的异步更新。但我同意你的看法，在90%的情况下，当请求完成时，打开的连接应该返回到池中。根据您使用的Web框架（Spring、DJANGO…），可以配置或至少以最少的工作量实现这种行为。
在关闭http连接的同时检查打开的连接会带来更多的开销，所以我想这就是为什么有些语言默认情况下不关闭它的原因。
如果不显式关闭它，则必须由垃圾收集器来完成，这可能需要一段时间。
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