Node is designed specifically TO facilitate long-running requests. There is only one thread (it's a single-threaded, evented system). Everything is done with callbacks, so if you have a long running I/O operation you'll just add a callback which completes the current HTTP response when the long-running I/O has finished. Node is quite happy to keep thousands of such callbacks around at once for massive concurrency.

Since Node scripts are persistent (i.e. aren't created and destroyed for each request), it doesn't care how long or how many connections are open. It's ideal for long-running requests.

I don't really have a direct answer to your question, but the somewhat official demo for node.js is a chat server that uses http long polling to push messages out, so node can definitely handle that.

I'm not sure, but I'd guess closing over it in the callback would work, as long as the TCP timeout is longer than the database response (even then, you could probably touch the stream every so often while you wait, perhaps via nextTick or something).