Without an index on source_id in the logs table the cron job for reports:expire takes several minutes, locks tables, and prevents Foreman from responding to ENC requests.

Adding an index eliminates all the above and reports:expire runs lickety split.

See discussion at: https://groups.google.com/forum/#!topic/foreman-dev/kBz1fjSIpeQ

Workaround (MySQL):
ALTER TABLE `logs` ADD INDEX `index_logs_on_source_id` (`source_id`);