Postgres 7.4.2 hanging when vacuum full is run

Hi -

This has been happening more recently. Our database hangs after a VACUUM
and is unresponsive when we come in next morning.

The vacuum job runs at 03:00 am daily.
The command is : /usr/local/pgsql/bin/vacuumdb --full -d DbName

Also, what exactly does this mean VACUUM waiting. Is there a reason why it
is never emerging from the VACUUM job?
I understand that doing a vacuumdb --full causes the tables to lock (not
really sure about the workings of vacuum).

Any light on this would be really appreciated.

Thanks,
Radhika

Below is what ps -ef |grep postgres shows:

5530 ? S 0:13 /usr/local/pgsql/bin/postmaster -i
5534 ? S 0:01 postgres: stats buffer process
5535 ? S 0:04 postgres: stats collector process
5621 ? S 0:53 postgres: slony myDB 10.142.20.50 idle
5626 ? S 0:51 postgres: slony myDB 10.142.20.50 idle
5627 ? S 0:34 postgres: slony myDB 10.142.20.50 idle
5628 ? S 5:40 postgres: slony myDB 10.142.20.50 idle
5637 ? S 2:09 postgres: slony myDB 10.132.20.26 idle
5638 ? S 1:56 postgres: slony myDB 10.132.20.26 idle
5745 ? S 42:08 postgres: abc myDB [local] idle
20774 ? S 4:29 postgres: abc myDB [local] idle
20775 ? S 0:00 postgres: abc myDB [local] idle in
transaction
20776 ? S 0:00 postgres: abc myDB [local] idle
17509 ? S 0:06 postgres: abc myDB [local] VACUUM waiting
24656 ? S 0:00 postgres: abc myDB [local] INSERT waiting
30489 ? S 0:00 postgres: abc myDB [local] SELECT waiting
30637 ? S 0:00 postgres: abc myDB [local] UPDATE waiting
30647 ? S 0:00 postgres: abc myDB [local] UPDATE waiting
30668 ? S 0:00 postgres: abc myDB [local] UPDATE waiting

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