Re: Deleting takes days, should I add some index?

Thank you, Pavel!

I didn't even think about trying to "explain analyze" deletion of just 1
record -

On Thu, Feb 25, 2021 at 10:04 PM Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
wrote:

> čt 25. 2. 2021 v 19:39 odesílatel Alexander Farber <
>> alexander(dot)farber(at)gmail(dot)com> napsal:
>>
>>> The question is why does the command take days (when I tried last time):
>>> delete from words_games where created < now() - interval '12 month';
>>>
>>>
>> postgres=# explain analyze delete from words_games where gid = 44877;
>>
>> create index on words_scores(mid);
>>
>
I have also added:

create index on words_puzzles(mid);

and then the result if finally good enough for my nightly cronjob:

explain analyze delete from words_games where created < now() - interval
'12 month';
QUERY PLAN

--------------------------------------------------------------------------------------------------------------------------
Delete on words_games (cost=0.00..49802.33 rows=104022 width=6) (actual
time=2121.475..2121.476 rows=0 loops=1)
-> Seq Scan on words_games (cost=0.00..49802.33 rows=104022 width=6)
(actual time=0.006..85.908 rows=103166 loops=1)
Filter: (created < (now() - '1 year'::interval))
Rows Removed by Filter: 126452
Planning Time: 0.035 ms
Trigger for constraint words_chat_gid_fkey on words_games: time=598.444
calls=103166
Trigger for constraint words_moves_gid_fkey on words_games: time=83745.244
calls=103166
Trigger for constraint words_scores_gid_fkey on words_games:
time=30638.420 calls=103166
Trigger for constraint words_puzzles_mid_fkey on words_moves:
time=15426.679 calls=3544242
Trigger for constraint words_scores_mid_fkey on words_moves:
time=18546.115 calls=3544242
Execution Time: 151427.183 ms
(11 rows)

There is one detail I don't understand in the output of "explain analyze" -
why do the lines

"Trigger for constraint words_scores_mid_fkey on words_moves: time=1885.372
calls=4"

completely disappear after adding the index? Are those the "ON DELETE
CASCADE" triggers?

Aren't they called after the index has been added?

Best regards
Alex