Re: Very slow Query compared to Oracle / SQL - Server

[Alexey M Boltenkov]

On 05/06/21 19:11, luis.robe...@siscobra.com.br wrote:
----- Mensagem original -----
De: "Semen Yefimenko" <semen.yefime...@gmail.com>
Para: "pgsql-performance" <pgsql-performance@lists.postgresql.org>
Enviadas: Quinta-feira, 6 de maio de 2021 11:38:39
Assunto: Very slow Query compared to Oracle / SQL - Server

SELECT column1,..., column54 where ((entrytype = 4000 or entrytype = 4001 or
entrytype = 4002) and (archivestatus <= 1)) order by timestampcol desc;
  

The first thing I would try is rewriting the query to:

SELECT column1,..., column54
   FROM logtable
  WHERE (entrytype in (4000,4001,4002))
    AND (archivestatus <= 1))
  ORDER BY timestampcol DESC;

Check if that makes a difference...

Luis R. Weck



The IN statement will probable result in just recheck condition change 
to entrytype = any('{a,b,c}'::int[]). Looks like dispersion of 
archivestatus is not enough to use index idx_arcstatus.

Please try to create partial index with condition like (archivestatus <= 
1) and rewrite select to use (archivestatus is not null and 
archivestatus <= 1).

CREATE INDEX idx_arcstatus_le1 ON schema.logtable ( archivestatus ) 
where (archivestatus <= 1) TABLESPACE tablespace;