Em ter., 28 de set. de 2021 às 12:40, Daniel Diniz <dan...@flashcourier.com.br>
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.
