Event logs are pruned once every 24 hours (at 2AM) to the last 1000 events per attribute attribute per device from what I've read. The other logs (not event logs) are not written to the DB, they're just a file from what I've read in this forum. If this is wrong, please correct me.
EDIT: Some sources:
The above is corrected in a post below. I should have read further in that thread.
