The site requires too many resources in a number of areas.
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The number one issue I see is there are way too many joins with out indexes required and this kills the database performance!
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Ideally there would be NO joins without indexes. This is just poor table layout and script design.
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The second issues that comes to mind is the way everything is broken down.
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Code reuse is great but all those includes add overhead for the web server.
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The number of javascript and css files (27) see more that must be downloaded is also an issues for the server and the clients.
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A default install of Dolphin 6.1.4 gives a 'Yahoo Performance Grade: F(39)' you can run this test on your own sites by downloading the YSlow plugin for FireFox...
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Its just sad that a 2 x 3.06Ghz server with 4GB of RAM and 6x 10K RPM SCSI drives with optimized mysql and php using eAccelerator I can only serve about 20 pages per second when testing the home page.
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The same server can server over 1200 'hello world' test pages per second!
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Anyway... Rant over.