General performance problem!

Hello,

I have a dedicated server for my posgresql database :

P4 2.4 GHZ
HDD IDE 7200 rpm
512 DDR 2700

I have a problem whith one table of my database :

CREATE SEQUENCE "base_aveugle_seq" START 1;
CREATE TABLE "base_aveugle" (
"record_id" integer DEFAULT nextval('"base_aveugle_seq"'::text) NOT NULL,
"dunsnumber" integer NOT NULL,
"cp" text NOT NULL,
"tel" text NOT NULL,
"fax" text NOT NULL,
"naf" text NOT NULL,
"siege/ets" text NOT NULL,
"effectif" integer NOT NULL,
"ca" integer NOT NULL,
Constraint "base_aveugle_pkey" Primary Key ("record_id")
);
CREATE INDEX base_aveugle_dunsnumber_key ON base_aveugle USING btree (dunsnumber);
CREATE INDEX base_aveugle_cp_key ON base_aveugle USING btree (cp);
CREATE INDEX base_aveugle_naf_key ON base_aveugle USING btree (naf);
CREATE INDEX base_aveugle_effectif_key ON base_aveugle USING btree (effectif);

This table contains 5 000 000 records

I have a PHP application which often makes queries on this table (especially on the "cp","naf","effectif" fields)

Querries are like :
select (distint cp) from base_aveugle where cp='201A' and effectif between 1 and 150
select (*) from base_aveugle where naf in ('721A','213F','421K') and cp in ('54210','21459','201A') and effectif < 150

I think it is possible to optimize the performance of this queries before changing the hardware (I now I will...) but I don't know how, even after having read lot of things about postgresql ...

Thanks ;)

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