buildfarm housekeeping / planning

The buildfarm is now going on six years old (time flies when you're
having fun!) and the database is now rather large - around 76Gb on disk.
We'd like to reduce that quite a lot, especially by purging out the logs
of old builds. And while the old data isn't publicly accessible, it has
occasionally been used to run specialised queries to research particular
issues. It's also arguably a useful historical resource that shouldn't
be lightly abandoned.

I'd like to get an idea of what the community regards as a reasonable
amount of data to keep online and readily handy? Six months worth? A
year? two years? Is it worth keeping logs of error stages longer than
successful stages? If so, what should the periods be?

One of the things that I'd like to be able to do is FTS on the logs.
Part of our plan is to move to a much more modern version of Postgres.
Keeping the logs to a reasonable size will possibly allow us to provide
FTS, although I haven't discussed that part with Josh Drake yet, and as
it's hosted at CMD he does get a say :-)

cheers

andrew