Large Objects: Sizeof and Deleting Unlinked LOs

Is there an SQL function to determine the size of a large object?

Also, can I safely delete all the large objects in
pg_catalog.pg_largeobject? For example:

select lo_unlink(loid) from (select distinct loid from
pg_catalog.pg_largeobject) as loids where loid not in (select my_oid
from my_only_table_that_uses_large_objects)

Or are there other things stored in there that I don't know about!

Thanks.

Howard Cole
www.selestial.com