You will need to verify which DB version you are using but the default embedded DB is (I believe) SQL Express 2005 which has a 4GB limit.
http://msdn.microsoft.com/en-us/library/ms345154%28v=sql.90%29.aspx
To manage your logs, you can set the number of days to keep events. Do this by going to the Admin Icon from any View and select System Settings. This will display 3 options for purging Real-time, Profile and Analysis events.
Also, make a backup and edit the the ...\Symantec\Critical System Protection\Server\tomcat\conf\sis-server.properties file. Uncomment the sisdbcleanup options and set them to the desired number of hours and the number of events to purge. You can monitor the size of the DB by using the custom Symantec queries built into the product. (Queries\Symantec\<policy pack version>\status\Database Status). Also,
Monitor the system deleting the events to ensure you are "throttling" them appropriatly. You may be creating events faster than you are deleting them in which case the DB will keep growing. Do an Event Search, choose Audit for the Event Category, enter the appropriate time frame to search and enter "DELETE EVENTS" without quotes into the Operation text box. In this event, make sure that the events deleted is less than the purge limit you set. If its consistently equal to the purge limit, its not deleting all the events it should and your DB will continue to grow.
To go a step further, you may want to setup an e-mail alert that will e-mail you the event for ongoing monitoring.
# sisdbcleanup.runtime
# sisdbcleanup.event.purge.limit
#
# sisdbcleanup.runtime
# This tag represents how often database cleanup is performed.
# The value is specified in hours, ex 24 means that database
# cleanup is performed every 24 hours.
#
# default: 23
#
#
# sisdbcleanup.event.purge.limit
# This tag represents the max number of event are purged each
# time the db cleanup is performed. This value will only be
# used when the event purging is enabled in the console.
#
# default: 100000
#sisdbcleanup.runtime=23
#sisdbcleanup.event.purge.limit=100000