help speeding up a query in postgres 8.4.5

Would really appreciate someone taking a look at the query below....
Thanks in advance!

this is on a linux box...
Linux dsrvr201.larc.nasa.gov 2.6.18-164.9.1.el5 #1 SMP Wed Dec 9
03:27:37 EST 2009 x86_64 x86_64 x86_64 GNU/Linux

explain analyze
select MIN(IV.STRTDATE), MAX(IV.ENDDATE)
from GRAN_VER GV
left outer join INVENTORY IV on GV.GRANULE_ID = IV.GRANULE_ID, INVSENSOR
INVS
where IV.INV_ID='65' and GV.GRANULE_ID = INVS.granule_id and
INVS.sensor_id='13'

"Aggregate (cost=736364.52..736364.53 rows=1 width=8) (actual
time=17532.930..17532.930 rows=1 loops=1)"
" -> Hash Join (cost=690287.33..734679.77 rows=336949 width=8)
(actual time=13791.593..17323.080 rows=924675 loops=1)"
" Hash Cond: (invs.granule_id = gv.granule_id)"
" -> Seq Scan on invsensor invs (cost=0.00..36189.41
rows=1288943 width=4) (actual time=0.297..735.375 rows=1277121 loops=1)"
" Filter: (sensor_id = 13)"
" -> Hash (cost=674401.52..674401.52 rows=1270865 width=16)
(actual time=13787.698..13787.698 rows=1270750 loops=1)"
" -> Hash Join (cost=513545.62..674401.52 rows=1270865
width=16) (actual time=1998.702..13105.578 rows=1270750 loops=1)"
" Hash Cond: (gv.granule_id = iv.granule_id)"
" -> Seq Scan on gran_ver gv (cost=0.00..75224.90
rows=4861490 width=4) (actual time=0.008..1034.885 rows=4867542 loops=1)"
" -> Hash (cost=497659.81..497659.81 rows=1270865
width=12) (actual time=1968.918..1968.918 rows=1270750 loops=1)"
" -> Bitmap Heap Scan on inventory iv
(cost=24050.00..497659.81 rows=1270865 width=12) (actual
time=253.542..1387.957 rows=1270750 loops=1)"
" Recheck Cond: (inv_id = 65)"
" -> Bitmap Index Scan on inven_idx1
(cost=0.00..23732.28 rows=1270865 width=0) (actual time=214.364..214.364
rows=1270977 loops=1)"
" Index Cond: (inv_id = 65)"
"Total runtime: 17533.100 ms"

some additional info.....
the table inventory is about 4481 MB and also has postgis types.
the table gran_ver is about 523 MB
the table INVSENSOR is about 217 MB

the server itself has 32G RAM with the following set in the postgres conf
shared_buffers = 3GB
work_mem = 64MB
maintenance_work_mem = 512MB
wal_buffers = 6MB

let me know if I've forgotten anything! thanks a bunch!!

Maria Wilson
NASA/Langley Research Center
Hampton, Virginia
m(dot)l(dot)wilson(at)nasa(dot)gov

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