To manually purge entries in the Delete Log database (ics50deletelog.db), use the cspurge utility:
cspurge -e endtime -s starttime
where 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 cspurge.