@All: Javascript wouldn't cause server performance issues on its own of course, any more than any other static files served out by Apache. (Though it can cause serious browser performance issues.) If the javascript dynamically formed and served out, or if it makes further server calls as it runs, then of course it could cause undue server loads, if not properly optimized.


@DolphinBugFixing: The amount of MySQL connections isn't as critical as the amount of MySQL queries. The XML.php file discussed see more earlier causes 4 MySQL queries every 5 seconds by default. On top of that, you will of course have an additional (and larger) amount of queries per page request as users browse your site — anywhere between ten to a few dozen (which is on the excessive side). Here's quick calculation for MySQL query loads per second:

1 user = (1 pageload x 18 queries / 120 sec interval) + (1 XML.php x 4 queries / 5 sec interval) = 0,15 qps + 0,8 qps = 0,95 qps

Then, 100 users would cause an average of 95 queries per second, which is on top of the Apache+PHP server load caused by the software. I wouldn't expect that to fly on a shared hosting account, unless the host is okay with your hogging up way more than you pay for. The RAM and CPU impact of the queries of course depends on how optimized they (and the database) are. (Aside possible MySQL caches etc., that shouldn't be relied on by programmers as primary solutions.)