8GB is nothing.
I had a server set to keep proxy logs for a couple of months and noticed the free space on the drive was a lot less than I thought should be so I set the logs to purge after a week and thought nothing more of it.
a few more months later and bam, 100GB db file!
I assume there's some kind of problem where the purge command times out if the db is too big so it never purges and the problem just snowballs.
I'd agree with some way of limiting the maximum size of the logs stored in the database, ideally with some method of archiving out the old logs to a compressed file.
Postgesql's ability to keep on working until it ran out of disc space was pretty impressive though.