Should a DB vacuum use up a lot of space ?

Hi all,

We’ve got a 16TB database that’s run up against the wrap-around tx id issue (despite running auto-vacuum):
ERROR: database is not accepting commands to avoid wraparound data loss in database "public"
HINT: Stop the postmaster and use a standalone backend to vacuum that database.

The message says to VACUUM the whole database so we’ve dropped down to single user mode and issued a “vacuum verbose” command on the backend

1) Unlike other times I’ve run vacuum verbose, I’m not getting any logging message at all (for the past 9 hours)

2) File system usage is going steadily up (3TB over the past 9 hours). Why is that ? I didn’t expect additional disk usage and we’re going to run into disk space usage if this keeps up.

3) Was a database-wide vacuum required or could I have just figured out which tables needed to be vacuumed and vacuumed those (my understanding was no), for example using http://dba.stackexchange.com/a/35234 and a query such as SELECT c.oid::regclass as table_name, greatest(age(c.relfrozenxid),age(t.relfrozenxid)) as age FROM pg_class c LEFT JOIN pg_class t ON c.reltoastrelid = t.oid WHERE c.relkind IN ('r', 'm') order by 2 desc limit 10;

4) Assuming I could have just identified individual tables that required vacuuming, can I CTRL-C the current vacuum process without running into issues ?

Thanks
Philippe Girolami