At this point there really isn't much of a debate; using Google's CDN to load jQuery isn't likely to benefit the majority of your first-time visitors. You're almost certainly better off bundling jQuery up with the rest of your site's JavaScript and making sure you're serving long-lived cache-controlling headers with it.

Upon investigation, we found that one view was responsible for most of that time.

However, the query execution itself was fast, around 11 ms.

But, the views rendering time was obscenely high: 2,603.48 ms!

So, when editing the view, you would see this at the bottom:

Query build time 2.07 ms
Query execute time 11.32 ms
View render time 2,603.48 ms
Since this view was on each page, in a block on the side bar, it was causing all the pages of the site to be slow.

The underlying reason was really bad coding in the views-view--viewname.tpl.php, which is too long to explain. But the gist of it is that the view returned several thousands rows of taxonomy terms, and was was supposed to render them in a tree. However, the actual view template just looped through the dataset and did not do much and displayed static HTML in the end!

The solution for this was quite simple: enable Views caching.

To do this, go to the view's Defaults, then Basic settings, then Caching. Change to Time Based, then select at least 1 hour for each of Query results and Rendered output.

Save the view, and you will see a positive impact on performance of your pages.

Drupal 7 can be used with Varnish and other reverse proxy servers if configured correctly. This blog post highlights how you can control your cache with Drupal, the Varnish module and the Cache Actions module.
Using a reverse proxy cache is an efficient way to cache your web site in order to get faster response times. Drupal 7 works with reverse proxy cache servers like Varnish out of the box and the integration can be extended by using the Varnish module. I'm going to show you how the integration works in this blog post.

En artikel om hur man enkelt bygger en cachefunktion för all output från ett PHP-script.