Better performance from WP Super Cache
If you use the WP Super Cache WordPress plugin (and you should, if you use WordPress), it has a settings page section titled “Expiry Time & Garbage Collection”. It sets the “Cache Timeout” to 3600 seconds by default, and warns that you should set it lower on a busy site.
That advice makes sense if you have a sudden surge of traffic to a single page. However, if your site is generally very busy across all pages (for example, if you have an archive of hundreds or thousands of posts that are constantly being indexed by search engines), we’ve found that you should do the opposite to improve performance: set it much higher. We recommend setting it to 172800 seconds (which is 48 hours). This can cut your CPU usage in half, which will speed up your site.
The reason for this is that when WP Super Cache creates a cached page, it wants to make sure that those pages don’t build up forever. Every ten minutes or so, it looks through them all and deletes any that are older than the “cache timeout”.
On some servers that use a network file system called “NFS”, looking through a large number of files causes performance problems. That’s why the WP Super Cache author recommends making them expire quickly: it reduces the number of files it has to examine each time.
On our servers, we don’t use NFS and looking through lots of files does not cause a performance problem. Leaving the files for a longer time is safe and increases the chance that a page will already be cached when it’s needed.
If you’re a Tiger Technologies customer who makes this change and you want to see how it affects the CPU usage, just let us know and we can provide you with details.
Updated 2013-06-11 to reflect that the plugin field is now named “Cache Timeout” instead of “Expiry Time”.