Calendar Server automatically creates the Delete Log database (ics50deletelog.db) in the csdb directory along with the other Calendar Server database files. Calendar Server writes events and todos to the Delete Log database as follows:
Non-Recurring Events and Todos
When a non-recurring event or todo is deleted, Calendar Server removes it from the Events database (ics50events.db) or Todos database (ics50todos.db) and then writes it to the Delete Log database (ics50deletelog.db).
Recurring Events and Todos
When individual instances of a recurring event or task are deleted, Calendar Server writes each deleted instance of the event or task to the Delete Log database (ics50deletelog.db).
When all instances of a recurring event or todo are deleted, Calendar Server deletes the master component from the event or todo database and then writes it to the Delete Log database. A master component in the Delete Log database will contain the rrules, rdates, exrules, and exdates recurrence parameters.