vacuuuuuuum!!!

hi all.
I'm here again.

to PostgreSQL DB, I'm using "vacuum" command in a file which is executed at
certain time
in a day by cron
the file is like follows;

psql inmsr <<EOF
delete from "TBL1" where "atime" < 'now';
commit;
delete from "TBL2" where "atime" < 'now';
commit;
delete from "TBL3" where "atime" < 'now';
commit;
vacuum analyze;
commit;

"delete" commands're done successfully, but when looking up the DB files
under /usr/local/pgsql/data/base/ ,
those tables still have some memories.
Also, keys that those tables have seem not to be deleted.

Does command "vacuum cannot clean up the keys ??
How can I "vacuum" up the memories??
OR, I might be wrong in a use of "vacuum" command.
could you tell me how it actually works?

what I want to do with this file is, to clean up the accumlated data from a
DB
once in a month, so that we can save memory.

I do aprreciate for your advise. thank you!

hiroko Ogawa
h_ogawa(at)rnk(dot)co(dot)jp