There is a strange bug with garbage collection. If I set Cache Timeout to 3600 seconds and Timer to 600 seconds, the settings will not save, and I continually get the following message banner:
Warning! Garbage collection is not scheduled!
Garbage collection by this plugin clears out expired and old cached pages on a regular basis. Use this form to enable it.
If I tell it to email me whenever garbage collection runs, it does email me every ten minutes, but lists zero files and directories as being deleted:
The WP Super Cache Garbage Collector has now run, deleting 0 files and directories.
If you want to switch off these emails please see the WP Super Cache Advanced Settings
page on your blog.
The Garbage Collector.
In order to dismiss the error message, I have to set the garbage collection to something other than 3600/600. Even 3600/601 works.
I am preloading the cache, if that matters.