pg_stat_activity is the place to look.
This tells you all of the blocked pids:
SELECT pid
, username
, pg_blocking_pids(pid) AS blocked_by
, left(query, 100) as blocked_query
FROM pg_stat_activity
WHERE CARDINALITY(blocking_pids(pid)) > 0;
From there, you can see what the blocking pid is doing.
On 2/2/23 12:21, Kenny Bachman wrote:
In fact, when I run the query for the second time, it returns very fast results. But after a while the problem reoccurs.
Not just for these queries, but almost all queries in the database are slowed down this way.
Is it normal to have a lock on the catalog or system tables? What should I do when this happens on pg_statistic or other catalogs?
thanks a lot for your comments and help
Kenny
Kenny Bachman <kenny.bachman17@gmail.com> writes:
> EXPLAIN ANALYZE select
> i."DefinitionId",
> from
> "T_WF_INSTANCE" i
> where
> i."InstanceId" = 10045683193;
> QUERY PLAN
> --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> Index Scan using
> "T_WF_INSTANCE_InstanceId_ApplicationCd_EntityStatusCd_idx" on
> "T_WF_INSTANCE" i (cost=0.57..2.79 rows=1 width=34) (actual
> time=2.522..2.522 rows=1 loops=1)
> Index Cond: ("InstanceId" = '10045683193'::bigint)
> * Planning Time: 8460.446 ms Execution Time: 2.616 ms*
> (4 rows)
It's hard to believe that such a simple query could take that
long to plan. What I'm wondering is if the planner got blocked
on some other session's exclusive lock. Not a lock on
"T_WF_INSTANCE" itself, because we'd have got that lock during
parsing before the "Planning Time" measurement starts. But
there's going to be a physical access to the table's index
to determine its tree height, so an ex-lock on the index could
explain this. Or an ex-lock on catalogs, particularly pg_statistic.
What else is going on in your database when this happens?
regards, tom lane
--
Born in Arizona, moved to Babylonia.