MyISAM database but all civicrm_ tables are INNODB... is this a problem?
I backed the database up, opened it up in Sequel Pro and went to the civicrm_system_log table. Under "Table Info" I could select "InnoDB" from the dropdown. Then I cleared the caches on the CiviCRM installation and the system status came back green ("System Status: OK").



Per a comment from George Lozier on another thread, the MySQL query to do the same is:

ALTER TABLE civicrm_system_log ENGINE=InnoDB;