This page contains historical information. It is probably no longer true.
Read the newest data retention and auto-purging criteria and implementation here:
Schemas that can be purged
These are the schemas that can be purged:
Should we move this to wikitech?
Sean Pringle scheduled the purging of data via the MariaDB using the Event Scheduler 
CREATE TABLE purge_schedule ( table_name varchar(100) NOT NULL, days tinyint(3) unsigned NOT NULL );
Then for each EL table you would do:
INSERT INTO purge_schedule VALUES ('MultimediaTiming_7193302', 30);