after vacuum, db is still "growing" :(

hi,

i'm using postgresql 7.4.8.

we have a database that only contains one table that contains session
data,

so it changes very often.

until now, we were vacuuming the database weekly.

it's current size is 15GB.

i know that when i once did a full-vacuum on this database, it's size
shrunk to 100MB.

so something is wrong there.
yesterday i did a vacuum, but in 5 hours, the database-size started to
grow again.

i don't understand this.

(well, there's always a possibility that we are "leaking" some db-rows
(means we are not deleting them from the db), but let's ignore that
possibility for now)

i know that a vacuum does not reclaim disk space...
after the vacuum the "real" db-size should become 100MB, and there
should be around 14.9GB "free" db-space. why isn't postgresql using that
space?

are there any cases, where a normal vacuum is unable to reclaim some
space, but a full-vacuum is able?

or any other ideas?

thanks,
gabor

--
That's life for you, said McDunn. Someone always waiting for someone
who never comes home. Always someone loving something more than that
thing loves them. And after awhile you want to destroy whatever
that thing is, so it can't hurt you no more.
-- R. Bradbury, "The Fog Horn"