Slow page loads - unable to determine the cause I am experiencing ~ 6 second page loads on every page of my Drupal 7 site. All of my scripts are loading from cache and relatively quickly except one, which will take 5.6-5.9 seconds to load (I am using FireBug to monitor):



Originally it looked to be the overlay.js javascript file, so I disabled the module. Then it was contextual.js with the exact same load time with everything else being quick. When I disabled that module it was yet another js library taking the same amount of time. This leads me to believe it has nothing to do with the libraries and is some other issue with the pages / rendering. I tried aggregating the JS and CSS, but the same issue was happening. All the queries showing up in my MySQL logs are executing relatively quickly (total of all query execution time is less than .5 seconds).

I am honestly at a loss for what to try. I suspect there is some problem here unrelated to loading any of the js files and that firebug is just reporting the delay as part of the last loaded file. This happens on both my custom pages and core drupal pages (like the modules and people screens). Is there any way to tell what is causing the long delay if it is not the javascript library?

EDIT: Details from the header for the script:

Request Headersview source
Accept  */*
Accept-Encoding gzip, deflate
Accept-Language en-US,en;q=0.5
Connection  keep-alive
Cookie  Drupal.toolbar.collapsed=0; __utma=163199651.1343774579.1355785168.1378243005.1379453429.30; __utmz=163199651.1378243005.29.5.utmcsr=google|utmccn=(organic)|utmcmd=organic|utmctr=(not%20provided); _ga=GA1.2.360149903.1357234390; SESSb5e5274d127f94079db0dc72d78d2200=AnQQv9Tp-NQT-b3YcVfOKzEnVSL-3cBexxbp2jY70D0; has_js=1
DNT 1
Host    example.com
If-Modified-Since   Wed, 03 Apr 2013 21:29:52 GMT
If-None-Match   "bcc-4d97b8dea7400"
Referer http://example.com/drupal/?q=peopleace/form/14172
User-Agent  Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Firefox/24.0

Response Headers From Cache
Accept-Ranges   bytes
Content-Length  3020
Content-Type    application/javascript
Date    Wed, 02 Oct 2013 19:26:36 GMT
Etag    "bcc-4d97b8dea7400"
Last-Modified   Wed, 03 Apr 2013 21:29:52 GMT
Server  Apache
If a 304 is taking 5+ seconds that means you webserver (most likely Apache) is being very slow. The ONLY other thing that could be causing this is if you have Far-Future enabled with the CDN module (and that's a stretch). Aggregating should help, as this will reduce the # of requests hitting Apache. 

What web server are you using? Also noticed that Clean-URLs is disabled so I would bet that the webserver needs to be configured.