Hmmm...correct me if I'm wrong, then.
If you had 1000 web browsers all hitting you with long AJAX wait times, then wouldn't each one require a separate thread on the server? How else does the server keep track of which request a given server "page" is responding to?
Maybe 1000 threads is okay on Apache and PHP, though.
Don't get me wrong: I *can* imagine a server-side architecture that could say "oh, that HTTP response isn't ready yet, so I'll just put it in a queue and use this thread for a different HTTP request." But does PHP actually *do* that?
I know I can do that with Java Servlets. Have done it, in fact. But I didn't think that PHP was that...well, "smart" is the wrong word. "Flexible", perhaps?
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A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.