Re: postgresql-14 slow query

On 4/15/22 16:59, Kenny Bachman wrote:
> Hello Team,
>
> How can I tune this query? It got even slower when I created the index
> for (state_id, order_id desc). The following explain analyze output is
> without an index. It takes 13 seconds if I create that index. Could
> you help me?
>
> Thank you so much for your help.
>
> SELECT DISTINCT ON (order_history.order_id) order_id,
> order_history.creation_date  AS c_date
> FROM work.order_history WHERE (order_history.state_id = ANY (ARRAY[30,
> 51, 63, 136, 195, 233, 348])) AND order_history.is_false = 0
> ORDER BY order_history.order_id DESC;
>
> EXPLAIN ANALYZE output:
>
>  Unique  (cost=672007.46..1519683.55 rows=206423 width=12) (actual
> time=1701.420..3439.095 rows=2049357 loops=1)
>    ->  Gather Merge  (cost=672007.46..1502346.48 rows=6934827
> width=12) (actual time=1701.419..2989.243 rows=6891551 loops=1)
>          Workers Planned: 4
>          Workers Launched: 4
>          ->  Sort  (cost=671007.40..675341.67 rows=1733707 width=12)
> (actual time=1657.609..1799.723 rows=1378310 loops=5)
>                Sort Key: order_id DESC
>                Sort Method: external merge  Disk: 38960kB
>                Worker 0:  Sort Method: external merge  Disk: 31488kB
>                Worker 1:  Sort Method: external merge  Disk: 36120kB
>                Worker 2:  Sort Method: external merge  Disk: 31368kB
>                Worker 3:  Sort Method: external merge  Disk: 36152kB
>                ->  Parallel Seq Scan on order_history
>  (cost=0.00..473993.00 rows=1733707 width=12) (actual
> time=0.041..1211.485 rows=1378310 loops=5)
>                      Filter: ((is_false = 0) AND (state_id = ANY
> ('{30,51,63,136,195,233,348}'::integer[])))
>                      Rows Removed by Filter: 3268432
>  Planning Time: 0.405 ms
>  Execution Time: 3510.433 ms

Parallel sequential scan of 1.7M rows, followed by a sort, all done in
3.5 sec? Doesn't look slow to me. Would indexing state_id be an option?

--
Mladen Gogala
Database Consultant
Tel: (347) 321-1217
https://dbwhisperer.wordpress.com