Hi All Recently I had many big data sites on Drupal , not surprising they are super slow. I'd like to share how I debug and my experience. PHP is quite CPU bound. So we can do apc or boost for performance. Mysql is memory bound, so I carefully set the mysql buffer size. There is another module called profiling, which I find panel and views content pane are so consuming, average 500 sql queries with 50000ms . So I rewrite in tpl files and it is much better. Drupal links: http://drupal.org/project/profiling http://drupal.org/project/apc http://drupal.org/project/boost Karl site: http://www.olivetuniversity.edu/
Install Varnish + memcached if your server capable to. It will improve the site loading. Remove drupal standard CSS, Utilize CSS3 as much as possible to replace image, embed image as base64 in css file if the image is very very small. These steps will improve load speed and CPU usage since less hit for Apache. Throw away any views that can be replaced by custom module + better sql queries. Nuke panels and replace it with custom tpl's. Be careful with node revision, if you have this enabled and forgot to clean old revision, large site can easily hogged down (imagine 1000 nodes X 20 revision = 20.000 table entry). Clean out unwanted modules, common Drupal mistake ==> Install Every module available since its free!. And many many more.....