Tom Lane a écrit :
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
Indeed, the tables I tried to vacuum have locks on them. AccessShareLock belonging to queries which seem sleeping. I tried to kill these queries but pg_cancel_backend() has no effect, and the process doesn't get the 15 signal.
How can I get rid of these blocking queries without restarting the server ? They are not listed as "waiting" in pg_stat_activity.
These queries are MOVE FORWARD on cursors, the underlying query is a rather complex one (unions, joins, functions calls)
Regards,
--
JC
Ph'nglui mglw'nafh Cthulhu n'gah Bill R'lyeh Wgah'nagl fhtagn!