We’ve got a lot of customers running WordPress, and we definitely recommend running WP Super Cache to improve performance. It can help dramatically!
But recently we’ve seen a number of our customers getting hammered by a ton of requests from FeedBurner. Usually the request is of this form:
/somepost?utm_source=feedburner&utm_medium=feed&utm_campaign=SomeCampaignString
We’ve also seen FeedBurner going crazy and making thousands of duplicate requests. One of the sites we host has gotten 45,000 simple status requests (HTTP “HEAD” requests) from FeedBurner today, for no good reason that we can see.
Unfortunately, the default rules of WP Super Cache prevent it from caching any request with a query that contains an equal sign. So all of these requests are being unnecessarily run freshly each time, rather than being served from the cache.
There’s an easy fix to this. Open your Web site’s .htaccess file. Look for the section of lines for WP Super Cache, and find the line which tests %{QUERY_STRING}. Insert this new line of text immediately above the existing line:
RewriteCond %{QUERY_STRING} utm_source= [OR]
The new line (ending with [OR]) must come before the existing %{QUERY_STRING} line. After inserting, the two lines should look exactly like this:
RewriteCond %{QUERY_STRING} utm_source= [OR]
RewriteCond %{QUERY_STRING} !.*=.*
There are four very similar blocks right next to each other in the .htaccess file. Be sure to add the new line to the same place in each block.
That’s the only change you’ll have to make! WP Super Cache will now be able to cache requests for normal pages that come from FeedBurner or Twitterfeed. If your Web site was being abused by FeedBurner (or Twitterfeed), you should see a definite improvement.
Update April 2012: Newer versions of the WP Super Cache plugin have four places that need to be changed, rather than two places. We’ve updated the post to reflect this.
Update October 2015: This post was updated to improve the RewriteCond rule so that more requests can be cached.