The other day we came under a DOS attack, just a brute force on our login page. The cache started flushing about every 20 seconds or so, which caused server load to spike pretty hard.
At the time I thought it may have been some odd get vars they were sending that did it, but today we have legitimite heavy load and it's happening again.
What would cause the cache to flush when I need it most?
We're not using WP comments, and it's happening far to often to be from people making posts.
We're running as a network install, and ALL the sites are flushing at once.