While I do not have much clarity into the schema and a lot of other insights, you might want to see my points below.
On Fri, Apr 15, 2022 at 4:59 PM Kenny Bachman <kenny.bachman17@xxxxxxxxx> 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)
Planner estimates vs actual rows seems to have some variation.
Firstly, have you manually updated statistics and verified if estimates can be almost near to actual ?
VACUUM ANALYZE work.order_history;
-> 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
Again, I am not suggesting a query rewrite or a change in schema (indexing or etc) as I do not have much clarity and thus not discussing it here.
However, setting a session level work_mem of 40MB should show some immediate difference.
SET work_mem TO '40MB';
<Run EXPLAIN ANALYZE again and check>
-> 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
