What is the "Formatted-messages cache" for and how does it operate?
The message cache works to help speed up your site, but should only be used if:
You have enough physical server memory for it.
Your site does not make use of any customizations, or built in options (like Ignore User), that alter the output of headings or messages. Doing so can result in unexpected results when a page is created.
There is a cache entry for each different combination of user class
(registered, guest, host, author). We cache the formatted message and drop it into the response page; we also cache discussion and folder headers.