Watch your pg_stats_* views before and after the delete and check what related tables have had lots of seqscans.


Mark Lewis wrote:

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 <[EMAIL PROTECTED]> 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

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