Watch your pg_stats_* views before and after the delete and check what
related tables have had lots of seqscans.
Chris
Mark Lewis wrote:
> Tom,
>
> I've got a similar problem with deletes taking a very long time. I know
> that there are lots of foreign keys referencing this table, and other
> foreign keys referencing those tables, etc. I've been curious, is there
> a way to find out how long the foreign key checks take for each
> dependent table?
>
> -- Mark Lewis
>
> On Thu, 2005-03-24 at 16:52, Tom Lane wrote:
>
>>Karim Nassar <Karim.Nassar@acm.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
>>
>>---------------------------(end of broadcast)---------------------------
>>TIP 7: don't forget to increase your free space map settings
>
>
>
> ---------------------------(end of broadcast)---------------------------
> TIP 9: the planner will ignore your desire to choose an index scan if your
> joining column's datatypes do not match