Actually, the error was pretty straightforward, and everything took less than a minute to fix as soon as the problem was brought to my attention.
It's not too perplexing either. The objectcache table is constantly being updated based on visits to different parts of the Encyclopedia, so if the mysql server is brought down (say, due to a power outage) in the middle of a query, that particular table is more likely to be corrupted, simply because only half of the transaction will have been processed.
Other members have reported some other errors that suggest the server we're on is having some hiccups (e.g. the backend httpd server that handles the main site crashed, so the proxying httpd server was giving 502 errors for a little while, and also our memcached process keeps getting reset, probably due to system restarts -- the current uptime on the server is only 14 hours).
