high load on server

Hello,

since 2 days ago we're facing an increased load on our database server
(opensuse10.3-64bit, PostgreSQL 8.3.5, 8GB Ram). This high load stays the whole
working day.
==================
current situation:
==================
#>top
top - 14:09:46 up 40 days,  8:08,  2 users,  load average: 7.60, 7.46, 7.13
...
Mem:   8194596k total,  5716680k used,  2477916k free,   185516k buffers
Swap:  4200988k total,      204k used,  4200784k free,  5041448k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
17478 postgres  15   0  610m 455m 444m R   52  5.7   0:08.78 postmaster
17449 postgres  15   0  606m 497m 489m S   37  6.2   0:16.35 postmaster
22541 postgres  16   0  607m 522m 516m R   31  6.5 123:25.17 postmaster
17491 postgres  15   0  618m 447m 435m S   22  5.6   0:03.97 postmaster
17454 postgres  15   0  616m 474m 457m S   18  5.9   0:15.88 postmaster
22547 postgres  15   0  608m 534m 527m S   18  6.7 100:12.01 postmaster
17448 postgres  16   0  616m 517m 501m S   17  6.5   0:15.60 postmaster
17451 postgres  15   0  611m 491m 479m S   11  6.1   0:25.04 postmaster
17490 postgres  15   0  606m 351m 344m S   10  4.4   0:02.69 postmaster
22540 postgres  15   0  607m 520m 513m S    2  6.5  33:46.47 postmaster
17489 postgres  15   0  604m 316m 311m S    2  4.0   0:03.34 postmaster


I assume the problem is caused by heavy writing slows down the
server....?!?...why?=>

1.) there are no long running queries:
SELECT   current_query, COUNT(current_query)
        FROM     pg_stat_activity
        WHERE    query_start < now() - interval '1 min'
        AND      current_query != '<IDLE>'
        GROUP BY current_query;
 current_query | count
---------------+-------
(0 Zeilen)


2.) we get wal archives written every 2-3min.
3.) we have no high-performant hardware layout, data and log on the same disk=>
#>iostat 2 5
Linux 2.6.22.5-31-default    03.04.2009
Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda              13,42        38,57       391,86  134436221 1365849137
Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda              36,21         0,00       994,02          0       2992
Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda              67,67         0,00      1621,33          0       4864
Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda              40,00         0,00       989,33          0       2968
Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda              26,91        18,60       948,84         56       2856

#>vmstat 2 10
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
 5  0    204 2449652 185692 5046168    0    0     2    24    1    1  2  0 95  2
 3  0    204 2448496 185692 5046184    0    0     0   518 2984 18683 24  5 65  6
 3  0    204 2430864 185692 5046192    0    0     0   344 2083 10004 34  3 58  5
 2  0    204 2434600 185700 5046200    0    0     0   386 2084 23592 33  3 57  7
 3  0    204 2425612 185700 5046220    0    0     0   372 2352 2905 36  2 57  5
 5  0    204 2424828 185700 5046256    0    0     0   600 2372 33094 36 12 48  4
 4  0    204 2405516 185700 5046256    0    0     4   992 1747 29035 33  8 52  6
 3  0    204 2419368 185708 5046272    0    0     4   660 2735 24732 36  7 51  6
 2  0    204 2419244 185712 5046296    0    0     0   360 2251 3193  9  1 84  5
 3  0    204 2407096 185712 5046296    0    0     0   332 2319 3269 20  3 72  5

Can I check further system/database details ?

Can we lower the load by reducing the amount of written wal archives, is this
somehow possible ?

Since buying and installing new hardware is a huge effort any other solutions
highly welcome :-))

thanks in advance...GERD...