Well, I tracked down our problem. I am one of those Xcart users that decided to add on more categoryids to the products table (4 more). However, with the new $category_condition statement under the func_search_products() function in func.php, all 8 of our categorids are searched instead of the old 3.5.7 method of just searching the first categoryid. On our remote linux web host this can result in a slow down of up to 144 seconds to procress that one segment of code in the func_search_products() function.
However, on our Windows testing server....it just dies. The SQL satement is so overwhelming that all of the CPU cycles are used up by mysqld-nt.exe to the the point that there isn't enough processing power to gather the database records from the hard drive which simply ceases to spin but once every 60 or so seconds.
So for those who did this modification to their Xcart, beware! I made the 'mistake' of correctly updating that $category_condition statement with our four additional categoryids.
It is now my task to find a way to improve that section of code and/or the structure of the products table, or devolve our cart back to 3.5.7.
