Apache 2.4 on Windows responds slowly, hangs when serving some dynamic pages

(I know the answer to this question. Posting this just to share the answer with the community)

My local (Windows 7) instance of Apache 2.4 experiences delays or hang-ups when serving some URLs, depending on which browser I use to access these URLs.

With Firefox/Chrome, Apache is slow to respond on certain URLs. The sluggishness occurs about 20% of the time on any given URL. When it does occur, there's a 5-second delay during which Firefox displays a "Waiting for..." status.

With Internet Explorer 9, Apache simply hangs and stops serving any requests (with any browser) until it is restarted.

• This seems to occur only with dynamic (PHP) requests, but not all of them. In fact, it only occurs on one specific site. Other PHP-based sites on the same machine work fine.


• It may or may not be significant that the problematic site consists of a large number of subdomains (VirtualHosts).


• Disabling the Windows Firewall and Comodo Firewall doesn't help.


• The problem seems more frequent with "busier" pages (additional requests for IFRAMES etc.)

I've tried many changes to httpd.conf (such as disabling KeepAlive, EnableMMAP, HostnameLookups) but nothing seems to work.