Lambda the Ultimate

For the record, events seem to have progressed something like this:

• An unusual spike of broken search bots and spam attempts created large numbers of session records, making the session table & indexes unusually large, reaching 6 times normal size, and creating high database contention.

  (As an aside, the search bot industry is to be commended on its inspiring reliance on recursion to construct request URLs. As soon as the authors learn how to either write a base case or use coinduction properly, we'll be all set, and bot-generated URLs will stop converging towards infinite length.)

• At some point, the session table index became corrupted (MySQL FTW?)
• Drupal was confused by the index problem, and overwrote the user and permissions records for the anonymous user (user id 0), something it is known to do in various situations. When in doubt, write to not-so-random places in the database!
• Anonymous users were prevented from accessing site content. This persisted for a number of hours, unnoticed. As Kanye West might say, in an accusatory tone, "LtU doesn't care about anonymous users!"
• Ultimately, the session index problem became bad enough to affect logged in users.
• A cry of anguish went up across the PL blogosphere, as if the evaluation of millions of lambdas had suddenly hit bottom. A crack team of roughnecks was flown to a secret base... Sorry, different story. Much investigation and a few SQL updates later, the problem was solved.