Re: Delete query takes exorbitant amount of time

Karim Nassar <Karim(dot)Nassar(at)acm(dot)org> writes:
> Here is the statement:

> orfs=# explain analyze DELETE FROM int_sensor_meas_type WHERE
> id_meas_type IN (SELECT * FROM meas_type_ids);
> QUERY PLAN
> -----------------------------------------------------------------------------------------------------------------------------
> Hash Join (cost=11.53..42.06 rows=200 width=6) (actual
> time=1.564..2.840 rows=552 loops=1)
> ...
> Total runtime: 2499616.216 ms
> (7 rows)

Notice that the actual join is taking 2.8 ms. The other ~40 minutes is
in operations that we cannot see in this plan, but we can surmise are ON
DELETE triggers.

> Where do I go from here?

Look at what your triggers are doing. My private bet is that you have
unindexed foreign keys referencing this table, and so each deletion
forces a seqscan of some other, evidently very large, table(s).

regards, tom lane