You can choose to manually purge entries in the Delete Log database (ics50deletelog.db), using the cspurge utility:
Usage of this utility is as follows:
cspurge -e endtime -s starttime
The variables endtime and starttime specify the ending and starting times in Zulu time (also referred to as GMT or UTC).
To run cspurge, you must be logged in as the user and group under which Calendar Server is running (defaults are icsuser and icsgroup) or as root.
For example, to purge entries from July 1, 2003 through July 31, 2003:
cspurge -e 20030731T235959Z -s 20030701T120000Z
For more information, see D.13 cspurge.