very slow execution of stored procedures

Greetings,

I found something very weird related with stored procedures execution. I
have this stored procedure to finalize a phone call, writing tha time of
call finalization and some other values to a calls table, called
cham_chamada. Please check this out (very simple) :

------------------------------------------------------------------

CREATE FUNCTION finaliza_chamv2(INT4, INT4, INT4, CHAR(23), CHAR(23),
CHAR(1),
INT4, INT4, INT4, CHAR(23), INT4, INT4,
CHAR(25),
INT4, INT4, INT4) RETURNS int4 AS
'
DECLARE
pbxs ALIAS FOR $1;
pchave ALIAS FOR $2;
pidentificacao ALIAS FOR $3;
pdtinicial ALIAS FOR $4;
pdtfinal ALIAS FOR $5;
pflgliber ALIAS FOR $6;
ptempototal ALIAS FOR $7;
pcodliber ALIAS FOR $8;
pddd ALIAS FOR $9;
pdtocup ALIAS FOR $10;
pindicadora ALIAS FOR $11;
pcategoria ALIAS FOR $12;
pidentidadea ALIAS FOR $13;
pfds ALIAS FOR $14;
presultcham ALIAS FOR $15;
pcifraorigem ALIAS FOR $16;

BEGIN

UPDATE cham_chamada
SET dt_final = TIMESTAMP(pdtfinal),
flg_liberacao = pflgliber,
temp_total = ptempototal,
cod_liberjuntor = pcodliber,
ddd = pddd,
indicadora = pindicadora,
cod_categoria = pcategoria,
identidadea = pidentidadea,
cod_fds = pfds,
cod_resultcham = presultcham,
cifra_origem = pcifraorigem
WHERE cod_bxs = pbxs AND
chave = pchave AND
identificacao = pidentificacao AND
dt_inicial = TIMESTAMP(pdtinicial);

IF pdtocup <> '''' THEN
UPDATE cham_servico
SET
dt_ocupacao = TIMESTAMP(pdtocup)
WHERE
cod_bxs = pbxs AND
chave = pchave AND
identificacao = pidentificacao AND
dt_inicial = TIMESTAMP(pdtinicial) AND
dt_finalizacao is null;
END IF;

RETURN 0;

END;
'
LANGUAGE 'plpgsql';

------------------------------------------------------------------

Once you know all about this stored procedure, lets see this call :
SELECT finaliza_chamv2(1,65535,49644,'2001-04-17 11:50:55','2001-04-17
12:17:40', '0', 0, 0, 48, '', 0, 10, '2817107', 0, 261, 65535);

If I change all variables to the parameters value inside the stored
procedure and then execute the frist script, then it is very fast, check out
:

bxs=#
bxs=# UPDATE cham_chamada
bxs-# SET dt_final = TIMESTAMP('2001-04-17 12:12:10'),
bxs-# flg_liberacao = '0',
bxs-# temp_total = 0,
bxs-# cod_liberjuntor = 0,
bxs-# ddd = 48,
bxs-# indicadora = 0,
bxs-# cod_categoria = 10,
bxs-# identidadea = '2817005',
bxs-# cod_fds = 0,
bxs-# cod_resultcham = 6,
bxs-# cifra_origem = 65535
bxs-# WHERE cod_bxs = 1 AND
bxs-# chave = 65535 AND
bxs-# identificacao = 49644 AND
bxs-# dt_inicial = TIMESTAMP('2001-04-17 12:12:00');
UPDATE 1

execution time : <1ms

now its time to do the same thing using the stored procedure :
bxs=#
bxs=# SELECT finaliza_chamv2(1,65535,49644,'2001-04-17 11:50:55','2001-04-17
12:17:40', '0', 0, 0, 48, '', 0, 10, '2817107', 0, 261, 65535);
finaliza_chamv2
-----------------
0
(1 row)

execution time : about 5s

Is it supose to execute with different speed? What can I do to fix it?

I'm using postgres RPM 7.0.3-2 in RedHat 6.2.

ps: There are some specific procedures I needed to execute before I got
pl/pgsql working :

CREATE FUNCTION plpgsql_call_handler ()
RETURNS opaque AS '/usr/lib/pgsql/plpgsql.so'
LANGUAGE 'C';

CREATE PROCEDURAL LANGUAGE 'plpgsql'
HANDLER plpgsql_call_handler
LANCOMPILER 'PL/PgSql internal';

Best regards from Brazil,

José Vilson de Mello de Farias
Dígitro Tecnologia Ltda - Brasil