Re: Problem with indices from 10 to 13

[Alan Hodgson <ahodgson@xxxxxxxxxxxxxxx>]

Em ter., 28 de set. de 2021 às 12:40, Daniel Diniz <daniel@xxxxxxxxxxxxxxxxxxx> escreveu:

Hello I migrated from postgres 10 to 13 and I noticed that there was a big increase in a querie that I use, I did explain in 10 and 13 and the difference is absurd, the indices and data are the same in 2. I've re-created and re-indexed but I don't know what changed from 10 to 13 which made the performance so bad, I don't know if it needs some extra parameter in some conf on 13.

Postgres 13

"QUERY PLAN"

"Limit  (cost=1.13..26855.48 rows=30 width=137) (actual time=10886.585..429803.463 rows=4 loops=1)"

"  ->  Nested Loop  (cost=1.13..19531164.71 rows=21819 width=137) (actual time=10886.584..429803.457 rows=4 loops=1)"

"        Join Filter: (h.ult_eve_id = ev.evento_id)"

"        Rows Removed by Join Filter: 252"

"        ->  Nested Loop  (cost=1.13..19457514.32 rows=21819 width=62) (actual time=10886.326..429803.027 rows=4 loops=1)"

"              ->  Nested Loop  (cost=0.85..19450780.70 rows=21819 width=55) (actual time=10886.259..429802.908 rows=4 loops=1)"

"                    ->  Index Scan Backward using hawbs_pkey on hawbs h  (cost=0.57..19444209.67 rows=21819 width=46) (actual time=10886.119..429802.676 rows=4 loops=1)"

"                          Filter: ((tipo_hawb_id = ANY ('{1,10,3}'::integer[])) AND ((nome_des)::text ~~* convert_from('\x255354455048414e592053544f4557204c45414e44524f25'::bytea, 'LATIN1'::name)))"

"                          Rows Removed by Filter: 239188096"

Index Scan Backward looks suspicious to me.

239,188,096  rows removed by filter it's a lot of work.

Do you, run analyze?

PostgreSQL has an unfortunate love of scanning the pkey index backwards when you use LIMIT.

Try pushing your actual query into a subquery (with an offset 0 to prevent it being optimized out) and then do the LIMIT outside it.