Postgresql Query is very Slow

Question

I have a table with 300000 rows and when i run a simple query like

   select * from diario_det;

it leaves 41041 ms to return rows. It's fine that? How i can optimize the query?

I use Postgresql 9.3 in Centos 7.

Here's is my table

CREATE TABLE diario_det
(
  cod_empresa numeric(2,0) NOT NULL,
  nro_asiento numeric(8,0) NOT NULL,
  nro_secue_pase numeric(4,0) NOT NULL,
  descripcion_pase character varying(150) NOT NULL,
  monto_debe numeric(16,3),
  monto_haber numeric(16,3),
  estado character varying(1) NOT NULL,
  cod_pcuenta character varying(15) NOT NULL,
  cod_local numeric(2,0) NOT NULL,
  cod_centrocosto numeric(4,0) NOT NULL,
  cod_ejercicio numeric(4,0) NOT NULL,
  nro_comprob character varying(15),
  conciliado_por character varying(10),
  CONSTRAINT fk_diario_det_cab FOREIGN KEY (cod_empresa, cod_local, cod_ejercicio, nro_asiento)
      REFERENCES diario_cab (cod_empresa, cod_local, cod_ejercicio, nro_asiento) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT fk_diario_det_pc FOREIGN KEY (cod_empresa, cod_pcuenta)
      REFERENCES plan_cuenta (cod_empresa, cod_pcuenta) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION
 )
WITH (
   OIDS=TRUE
);
 ALTER TABLE diario_det
   OWNER TO postgres;

-- Index: pk_diario_det_ax

-- DROP INDEX pk_diario_det_ax;

 CREATE INDEX pk_diario_det_ax
   ON diario_det
   USING btree
   (cod_pcuenta COLLATE pg_catalog."default", cod_local, estado COLLATE pg_catalog."default");

Answer 1

Very roughly size of one row is 231 bytes, times 300000... It's 69300000 bytes (~69MB) that has to be transferred from server to client.

I think that 41 seconds is a bit long, but still the query has to be slow because of amount of data that has to be loaded from disk and transferred.

You can optimise query by

• selecting just columns you that are going to use not all of them (if you need just cod_empresa it would reduce total amount of transferred data to ~1.2MB, but server would still have to iterate trough all records - slow)
• filter only rows that are going to use - using WHERE on columns with indexes can really speed the query up

If you want to know what is happening in your query, play around with EXPLAIN and EXPLAIN EXECUTE .

Also, if you're running dedicated database server, be sure to configure it properly to use a lot of system resources .