Hi,
This is one of the most painfull issues with DLP system (data is keep growing and demands more storage).
We udnerstood it one year ago, that we suddenly discover we are out of space, since DLP Tables took 250 GB!!!
This year we were smarter.
With the help of our briliant DBA's:
1. we took the tables
2. copy them to our test enviornment
3. load them to the app and ensure the data is correct
4. Then DBA took some actions in order to compress the data, which provide us another 100 GB on same table space
5. Then they did same process on production, Of course that it demands downtime
If you want, I can try and ask the the full procedure since i asked them to document it.
Anyway
what we are doing as well is to keep only 6 months incidents, we archive all other incidents and delete them (after we ensure that we have backup).
Once you delete incindets, some of the incidents will be written on the space which was used by the incidents you deleted (but not all of it, it's something related to how DLP built and Oracle tables)...
Good Luck