Join over two tables of 50K records takes 2 hours

Hi all,
I am running 9.03 with the settings listed below. I have a prohibitively slow query in an application which has an overall good performance:

select
    cast (SD.detectorid as numeric),
    CAST( ( (SD.createdtime - 0 )/ 18000000000000::bigint ) AS numeric) as timegroup,
    sum(datafromsource)+sum(datafromdestination) as numbytes,
    CAST ( sum(packetsfromsource)+sum(packetsfromdestination) AS numeric) as numpackets
from
    appqosdata.icmptraffic SD , appqosdata.icmptraffic_classes CL
where
    SD.detectorid >= 0 
    and CL.detectorid = SD.detectorid
    and CL.sessionid = SD.sessionid 
    and CL.createdtime = SD.createdtime 
    and SD.detectorid = 1
    and SD.createdtime >= 1317726000000000000::bigint and SD.createdtime < 1318326120000000000::bigint
    and CL.sessionid < 1318326120000000000::bigint
    and CL.classid = 1
group by
    SD.detectorid, timegroup

appqosdata.icmptraffic and appqosdata.icmptraffic_classes are both partitioned.

CREATE TABLE appqosdata.icmptraffic
(
    detectorid smallint not null default(0), -- references appqosdata.detectors(id),
    sessionid bigint not null,
    createdtime bigint not null,

...
   --primary key(detectorid, sessionid, createdtime)  defined in the children tables
);

CREATE TABLE appqosdata.icmptraffic_classes
(
    detectorid smallint not null,
    sessionid bigint not null,
    createdtime bigint not null,

    classid integer not null

   -- definitions in the children tables:
    --primary key(detectorid, sessionid, createdtime, classid)
    --foreign key(detectorid, sessionid, createdtime)  references appqosdata.icmptraffic(detectorid, sessionid, createdtime),
    --foreign key(classid) references appqosdata.display_classes(id),
);

"HashAggregate  (cost=154.24..154.28 rows=1 width=34) (actual time=7594069.940..7594069.983 rows=19 loops=1)"
"  Output: (sd.detectorid)::numeric, ((((sd.createdtime - 0) / 18000000000000::bigint))::numeric), (sum(sd.datafromsource) + sum(sd.datafromdestination)), ((sum(sd.packetsfromsource) + sum(sd.packetsfromdestination)))::numeric, sd.detectorid"
"  ->  Nested Loop  (cost=0.00..154.23 rows=1 width=34) (actual time=0.140..7593838.258 rows=50712 loops=1)"
"        Output: sd.detectorid, sd.createdtime, sd.datafromsource, sd.datafromdestination, sd.packetsfromsource, sd.packetsfromdestination, (((sd.createdtime - 0) / 18000000000000::bigint))::numeric"
"        Join Filter: ((sd.sessionid = cl.sessionid) AND (sd.createdtime = cl.createdtime))"
"        ->  Append  (cost=0.00..88.37 rows=7 width=18) (actual time=0.063..333.355 rows=51776 loops=1)"
"              ->  Seq Scan on appqosdata.icmptraffic_classes cl  (cost=0.00..37.48 rows=1 width=18) (actual time=0.013..0.013 rows=0 loops=1)"
"                    Output: cl.detectorid, cl.sessionid, cl.createdtime"
"                    Filter: ((cl.sessionid < 1318326120000000000::bigint) AND (cl.detectorid = 1) AND (cl.classid = 1))"
"              ->  Index Scan using icmptraffic_classes_10_pkey on appqosdata.icmptraffic_classes_10 cl  (cost=0.00..8.36 rows=1 width=18) (actual time=0.046..14.205 rows=3985 loops=1)"
"                    Output: cl.detectorid, cl.sessionid, cl.createdtime"
"                    Index Cond: ((cl.detectorid = 1) AND (cl.sessionid < 1318326120000000000::bigint) AND (cl.classid = 1))"
"              ->  Index Scan using icmptraffic_classes_11_pkey on appqosdata.icmptraffic_classes_11 cl  (cost=0.00..8.62 rows=1 width=18) (actual time=0.038..52.757 rows=14372 loops=1)"
"                    Output: cl.detectorid, cl.sessionid, cl.createdtime"
"                    Index Cond: ((cl.detectorid = 1) AND (cl.sessionid < 1318326120000000000::bigint) AND (cl.classid = 1))"
"              ->  Index Scan using icmptraffic_classes_12_pkey on appqosdata.icmptraffic_classes_12 cl  (cost=0.00..8.60 rows=1 width=18) (actual time=0.033..47.845 rows=13512 loops=1)"
"                    Output: cl.detectorid, cl.sessionid, cl.createdtime"
"                    Index Cond: ((cl.detectorid = 1) AND (cl.sessionid < 1318326120000000000::bigint) AND (cl.classid = 1))"
"              ->  Index Scan using icmptraffic_classes_13_pkey on appqosdata.icmptraffic_classes_13 cl  (cost=0.00..8.59 rows=1 width=18) (actual time=0.030..46.504 rows=13274 loops=1)"
"                    Output: cl.detectorid, cl.sessionid, cl.createdtime"
"                    Index Cond: ((cl.detectorid = 1) AND (cl.sessionid < 1318326120000000000::bigint) AND (cl.classid = 1))"
"              ->  Index Scan using icmptraffic_classes_14_pkey on appqosdata.icmptraffic_classes_14 cl  (cost=0.00..8.43 rows=1 width=18) (actual time=0.025..22.868 rows=6633 loops=1)"
"                    Output: cl.detectorid, cl.sessionid, cl.createdtime"
"                    Index Cond: ((cl.detectorid = 1) AND (cl.sessionid < 1318326120000000000::bigint) AND (cl.classid = 1))"
"              ->  Index Scan using icmptraffic_classes_15_pkey on appqosdata.icmptraffic_classes_15 cl  (cost=0.00..8.30 rows=1 width=18) (actual time=0.014..0.014 rows=0 loops=1)"
"                    Output: cl.detectorid, cl.sessionid, cl.createdtime"
"                    Index Cond: ((cl.detectorid = 1) AND (cl.sessionid < 1318326120000000000::bigint) AND (cl.classid = 1))"
"        ->  Materialize  (cost=0.00..65.13 rows=6 width=42) (actual time=0.001..73.261 rows=50915 loops=51776)"
"              Output: sd.detectorid, sd.createdtime, sd.datafromsource, sd.datafromdestination, sd.packetsfromsource, sd.packetsfromdestination, sd.sessionid"
"              ->  Append  (cost=0.00..65.10 rows=6 width=42) (actual time=0.059..244.693 rows=50915 loops=1)"
"                    ->  Seq Scan on appqosdata.icmptraffic sd  (cost=0.00..22.60 rows=1 width=42) (actual time=0.001..0.001 rows=0 loops=1)"
"                          Output: sd.detectorid, sd.createdtime, sd.datafromsource, sd.datafromdestination, sd.packetsfromsource, sd.packetsfromdestination, sd.sessionid"
"                          Filter: ((sd.detectorid >= 0) AND (sd.createdtime >= 1317726000000000000::bigint) AND (sd.createdtime < 1318326120000000000::bigint) AND (sd.detectorid = 1))"
"                    ->  Index Scan using icmptraffic_10_pkey on appqosdata.icmptraffic_10 sd  (cost=0.00..8.35 rows=1 width=42) (actual time=0.053..7.807 rows=3997 loops=1)"
"                          Output: sd.detectorid, sd.createdtime, sd.datafromsource, sd.datafromdestination, sd.packetsfromsource, sd.packetsfromdestination, sd.sessionid"
"                          Index Cond: ((sd.detectorid >= 0) AND (sd.detectorid = 1) AND (sd.createdtime >= 1317726000000000000::bigint) AND (sd.createdtime < 1318326120000000000::bigint))"
"                    ->  Index Scan using icmptraffic_11_pkey on appqosdata.icmptraffic_11 sd  (cost=0.00..8.59 rows=1 width=42) (actual time=0.025..27.957 rows=14372 loops=1)"
"                          Output: sd.detectorid, sd.createdtime, sd.datafromsource, sd.datafromdestination, sd.packetsfromsource, sd.packetsfromdestination, sd.sessionid"
"                          Index Cond: ((sd.detectorid >= 0) AND (sd.detectorid = 1) AND (sd.createdtime >= 1317726000000000000::bigint) AND (sd.createdtime < 1318326120000000000::bigint))"
"                    ->  Index Scan using icmptraffic_12_pkey on appqosdata.icmptraffic_12 sd  (cost=0.00..8.58 rows=1 width=42) (actual time=0.027..26.217 rows=13512 loops=1)"
"                          Output: sd.detectorid, sd.createdtime, sd.datafromsource, sd.datafromdestination, sd.packetsfromsource, sd.packetsfromdestination, sd.sessionid"
"                          Index Cond: ((sd.detectorid >= 0) AND (sd.detectorid = 1) AND (sd.createdtime >= 1317726000000000000::bigint) AND (sd.createdtime < 1318326120000000000::bigint))"
"                    ->  Index Scan using icmptraffic_13_pkey on appqosdata.icmptraffic_13 sd  (cost=0.00..8.56 rows=1 width=42) (actual time=0.030..26.075 rows=13430 loops=1)"
"                          Output: sd.detectorid, sd.createdtime, sd.datafromsource, sd.datafromdestination, sd.packetsfromsource, sd.packetsfromdestination, sd.sessionid"
"                          Index Cond: ((sd.detectorid >= 0) AND (sd.detectorid = 1) AND (sd.createdtime >= 1317726000000000000::bigint) AND (sd.createdtime < 1318326120000000000::bigint))"
"                    ->  Index Scan using icmptraffic_14_pkey on appqosdata.icmptraffic_14 sd  (cost=0.00..8.41 rows=1 width=42) (actual time=0.027..11.040 rows=5604 loops=1)"
"                          Output: sd.detectorid, sd.createdtime, sd.datafromsource, sd.datafromdestination, sd.packetsfromsource, sd.packetsfromdestination, sd.sessionid"
"                          Index Cond: ((sd.detectorid >= 0) AND (sd.detectorid = 1) AND (sd.createdtime >= 1317726000000000000::bigint) AND (sd.createdtime < 1318326120000000000::bigint))"
"Total runtime: 7594071.137 ms"



             name             |                                             current_setting                                             
------------------------------+----------------------------------------------------------------------------------------------------------
 version                      | PostgreSQL 9.0.3 on amd64-portbld-freebsd8.0, compiled by GCC cc (GCC) 4.2.1 20070719  [FreeBSD], 64-bit
 autovacuum                   | on
 autovacuum_analyze_threshold | 500000
 autovacuum_max_workers       | 1
 autovacuum_naptime           | 1h
 autovacuum_vacuum_threshold  | 500000
 checkpoint_segments          | 64
 effective_cache_size         | 3GB
 fsync                        | on
 lc_collate                   | C
 lc_ctype                     | C
 listen_addresses             | *
 log_destination              | syslog, stderr
 log_min_duration_statement   | 5ms
 log_rotation_age             | 1d
 log_rotation_size            | 100MB
 logging_collector            | on
 max_connections              | 30
 max_stack_depth              | 2MB
 server_encoding              | UTF8
 shared_buffers               | 1793MB
 silent_mode                  | on
 synchronous_commit           | on
 syslog_facility              | local0
 TimeZone                     | Europe/Jersey
 update_process_title         | off
 wal_buffers                  | 128kB
 work_mem                     | 24MB

Thanks for any help,
Svetlin Manavski