help with too slow query

Hello,
I have this table definition:
CREATE TABLE ism_floatvalues
(
id_signal bigint NOT NULL, -- Indica la señal a la que pertenece este
valor. Clave foránea que referencia al campo id_signal de la tabla
ism_signal.
time_stamp timestamp without time zone NOT NULL, -- Marca de tiempo
que indica fecha y hora correpondiente a este dato. Junto con id_signal
forma la clave primaria de esta tabla
var_value double precision, -- Almacena el valor concreto de la señal
en la marca de tiempo espeficicada.
CONSTRAINT ism_floatvalues_id_signal_fkey FOREIGN KEY (id_signal)
REFERENCES ism_signal (id_signal) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE CASCADE
)
WITH (
OIDS=FALSE
);

CREATE INDEX ism_floatvalues_index_idsignal_timestamp
ON ism_floatvalues
USING btree
(id_signal, time_stamp DESC);

*********************************************

Then I run this query....
*********************************************
EXPLAIN analyze
select round(CAST(sum(var_value) AS numeric),2) as var_value,
date_trunc('month', time_stamp) as time_stamp ,
date_part('month',date_trunc('month', time_stamp)) as month,
date_part('year',date_trunc('year', time_stamp)) as year from
ism_floatvalues where id_signal in
(
select id_signal from ism_signal where reference = 'EDCA' and id_source in
(
select id_source from ism_installation where id_installation in
(select id_installation from ism_groupxinstallation where id_group = 101)
)
)
and time_stamp > date_trunc('month', current_date - interval '11 months')
group by date_trunc('month', time_stamp), month, year
order by time_stamp

******************************
And this is the result:
******************************

"GroupAggregate (cost=4766541.62..4884678.62 rows=39483 width=16)
(actual time=1302542.073..1302713.154 rows=10 loops=1)"
" -> Sort (cost=4766541.62..4789932.12 rows=9356201 width=16) (actual
time=1302444.324..1302531.447 rows=9741 loops=1)"
" Sort Key: (date_trunc('month'::text,
ism_floatvalues.time_stamp)), (date_part('month'::text,
date_trunc('month'::text, ism_floatvalues.time_stamp))),
(date_part('year'::text, date_trunc('year'::text,
ism_floatvalues.time_stamp)))"
" Sort Method: quicksort Memory: 941kB"
" -> Hash Join (cost=545.65..3203518.39 rows=9356201 width=16)
(actual time=458941.090..1302245.307 rows=9741 loops=1)"
" Hash Cond: (ism_floatvalues.id_signal =
ism_signal.id_signal)"
" -> Seq Scan on ism_floatvalues (cost=0.00..2965077.57
rows=28817098 width=24) (actual time=453907.600..1002381.652
rows=29114105 loops=1)"
" Filter: (time_stamp > date_trunc('month'::text,
(('now'::text)::date - '11 mons'::interval)))"
" -> Hash (cost=544.19..544.19 rows=117 width=8) (actual
time=733.782..733.782 rows=40 loops=1)"
" Buckets: 1024 Batches: 1 Memory Usage: 2kB"
" -> HashAggregate (cost=543.02..544.19 rows=117
width=8) (actual time=733.072..733.412 rows=40 loops=1)"
" -> Hash Semi Join (cost=27.61..542.73
rows=117 width=8) (actual time=638.175..687.934 rows=40 loops=1)"
" Hash Cond: (ism_signal.id_source =
ism_installation.id_source)"
" -> Bitmap Heap Scan on ism_signal
(cost=18.84..530.42 rows=850 width=16) (actual time=243.690..284.303
rows=850 loops=1)"
" Recheck Cond: ((reference)::text
= 'EDCA'::text)"
" -> Bitmap Index Scan on
ism_signal_idx_reference (cost=0.00..18.63 rows=850 width=0) (actual
time=243.429..243.429 rows=865 loops=1)"
" Index Cond:
((reference)::text = 'EDCA'::text)"
" -> Hash (cost=8.27..8.27 rows=40
width=8) (actual time=394.393..394.393 rows=40 loops=1)"
" Buckets: 1024 Batches: 1 Memory
Usage: 2kB"
" -> Hash Semi Join
(cost=3.25..8.27 rows=40 width=8) (actual time=391.966..394.000 rows=40
loops=1)"
" Hash Cond:
(ism_installation.id_installation = ism_groupxinstallation.id_installation)"
" -> Seq Scan on
ism_installation (cost=0.00..4.17 rows=117 width=16) (actual
time=0.086..1.354 rows=117 loops=1)"
" -> Hash (cost=2.75..2.75
rows=40 width=8) (actual time=390.274..390.274 rows=40 loops=1)"
" Buckets: 1024
Batches: 1 Memory Usage: 2kB"
" -> Seq Scan on
ism_groupxinstallation (cost=0.00..2.75 rows=40 width=8) (actual
time=389.536..389.903 rows=40 loops=1)"
" Filter:
(id_group = 101)"
"Total runtime: 1302731.013 ms"

This query is very slow as you can see, it took about 20 minutos to
complete.... Can someone help me to improve performance on this query??
Regards.
--
Documento sin título

**Pedro Jiménez Pérez
**p(dot)jimenez(at)ismsolar(dot)com

****

**Innovación en Sistemas de Monitorización, S.L.**
Edificio Hevimar
C/ Iván Pavlov 2 y 4 - Parcela 4 2ª Planta Local 9
Parque Tecnológico de Andalucía
29590 Campanillas (Málaga)
Tlfno. 952 02 07 13
contacto(at)ismsolar(dot)com

firma_gpt.jpg, 1 kB

Antes de imprimir, piensa en tu responsabilidad y compromiso con el
MEDIO AMBIENTE!

Before printing, think about your responsibility and commitment with the
ENVIRONMENT!

CLÁUSULA DE CONFIDENCIALIDAD.- Este mensaje, y en su caso, cualquier
fichero anexo al mismo, puede contener información confidencial o
legalmente protegida (LOPD 15/1999 de 13 de Diciembre), siendo para uso
exclusivo del destinatario. No hay renuncia a la confidencialidad o
secreto profesional por cualquier transmisión defectuosa o errónea, y
queda expresamente prohibida su divulgación, copia o distribución a
terceros sin la autorización expresa del remitente. Si ha recibido este
mensaje por error, se ruega lo notifique al remitente enviando un
mensaje al correo electrónico contacto(at)ismsolar(dot)com y proceda
inmediatamente al borrado del mensaje original y de todas sus copias.
Gracias por su colaboración.