Re: vacuum won't even start

Jean-Christophe Praud <jc@steek.com> writes:
> I've a problem on a heavy loaded database: vacuums don't work since
> about a week. All I got is:

> mybase=# vacuum verbose analyze public.mytable;
> INFO:  vacuuming "public.mytable"
> (I stop it after hours)

> Looking with top and iotop, I see the process takes some cpu and disk io
> time during several minutes, then it seems to fall asleep.
> The process isn't locked according to pg_stat_activity.

When vacuum wants to clean up a particular table page, it will wait
until no other process is examining that page; and this wait is not
visible in pg_locks.  Perhaps you have got some queries referencing
those tables that have stopped midway and are just sitting?

Although pg_locks won't immediately show the wait, it could be useful
to help identify the culprit --- look for other processes holding
any type of lock on the table the vacuum is stuck on, and then go to
pg_stat_activity to see how old their current query is.

            regards, tom lane