simple select-statement takes more than 25 sec

Hi all

I have a table with ca. 4Mio Rows.

here is my simple select-statement:
SELECT * FROM CUSTOMER WHERE CUSTOMER_ID=5

the result appears after about 27 sec.

what's wrong?

the same statement on mysql takes 1 milisec.

please help

here is the structur of the table
CREATE TABLE public.customer
(
customer_id bigserial NOT NULL,
cooperationpartner_id int8 NOT NULL DEFAULT 0::bigint,
maincontact_id int8 NOT NULL DEFAULT 0::bigint,
companycontact_id int8,
def_paymentdetails_id int8,
def_paymentsort_id int8,
def_invoicing_id int8,
int_customernumber varchar(50),
ext_customernumber varchar(50),
CONSTRAINT customer_pkey PRIMARY KEY (customer_id),
CONSTRAINT customer_ibfk_1 FOREIGN KEY (cooperationpartner_id)
REFERENCES public.cooperationpartner (cooperationpartner_id) ON UPDATE
NO ACTION ON DELETE NO ACTION,
CONSTRAINT customer_ibfk_2 FOREIGN KEY (maincontact_id) REFERENCES
public.contact (contact_id) ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT customer_ibfk_3 FOREIGN KEY (companycontact_id) REFERENCES
public.contact (contact_id) ON UPDATE NO ACTION ON DELETE NO ACTION,
CONSTRAINT customer_ibfk_4 FOREIGN KEY (def_paymentdetails_id)
REFERENCES public.paymentdetails (paymentdetails_id) ON UPDATE NO ACTION
ON DELETE NO ACTION,
CONSTRAINT customer_ibfk_5 FOREIGN KEY (def_paymentsort_id) REFERENCES
public.paymentsort (paymentsort_id) ON UPDATE NO ACTION ON DELETE NO
ACTION,
CONSTRAINT customer_ibfk_6 FOREIGN KEY (def_invoicing_id) REFERENCES
public.invoicing (invoicing_id) ON UPDATE NO ACTION ON DELETE NO ACTION
) WITH OIDS;