Ineffective refresh of book/calendar meta backends
When an online calendar is sychronize at the defined interval it causes "massive" I/O operations.
It seems after every event insertion/update a sync operation gets executed on the filesystem.
Reproducible in evolution with e.g. http://calendar.google.com/calendar/ical/mozilla.com_dbq84anr9i8tcnmhabatstv5co%40group.calendar.google.com/public/basic.ics and forcing a synchronize.