Looks like https://petitions.whitehouse.gov is using MongoDB
Additional uncaught exception thrown while handling exception.
Original
MongoCursorException: couldn't send command in Mongo->__construct() (line 35 of /mnt/codebase/petition-release-2012-07-11/sites/all/modules/contrib/mongodb/mongodb.module).
Additional
MongoCursorTimeoutException: cursor timed out (timeout: 30000, time left: 0:0, status: 0) in MongoCollection->findOne() (line 22 of /mnt/codebase/petition-release-2012-07-11/sites/all/modules/contrib/mongodb/mongodb_cache/mongodb_cache.inc).