Interpreting vmstat

Hello,
(note best viewed in fixed-width font)

I'm still trying to find where my performance bottle neck is...
I have 4G ram, PG 7.3.4
shared_buffers = 75000
effective_cache_size = 75000

Run a query I've been having trouble with and watch the output of vmstat
(linux):

$ vmstat 1
procs memory swap io system
cpu
r b w swpd free buff cache si so bi bo in cs us
sy id
0 0 0 148 8732 193652
2786668 0 0 0 0 292 151 0 2 98
2 0 2 148 7040 193652
2786668 0 0 0 208 459 697 45 10 45
0 0 0 148 9028 193652
2786684 0 0 16 644 318 613 25 4 71
1 0 0 148 5092 193676
2780196 0 0 12 184 441 491 37 5 58
0 1 0 148 5212 193684
2772512 0 0 112 9740 682 1063 45 12 43
1 0 0 148 5444 193684
2771584 0 0 120 4216 464 1303 44 3 52
1 0 0 148 12232 193660
2771620 0 0 244 628 340 681 43 20 38
1 0 0 148 12168 193664
2771832 0 0 196 552 332 956 42 2 56
1 0 0 148 12080 193664
2772248 0 0 272 204 371 201 40 1 59
1 1 0 148 12024 193664
2772624 0 0 368 0 259 127 42 3 55

Thats the first 10 lines or so... the query takes 60 seconds to run.

I'm confused on the bo & bi parts of the io:
IO
bi: Blocks sent to a block device (blocks/s).
bo: Blocks received from a block device (blocks/s).

yet it seems to be opposite of that... bi only increases when doing a
largish query, while bo also goes up, I typically see periodic bo numbers
in the low 100's, which I'd guess are log writes.

I would think that my entire DB should end up cached since a raw pg_dump
file is about 1G in size, yet my performance doesn't indicate that that is
the case... running the same query a few minutes later, I'm not seeing a
significant performance improvement.

Here's a sample from iostat while the query is running:

$ iostat -x -d 1

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz
avgqu-sz await svctm %util
sda 0.00 0.00 0.00 0.00 0.00 0.00 0.00
42949552.96 0.00 0.00 100.00
sda1 0.00 0.00 0.00 0.00 0.00 0.00 0.00
42949662.96 0.00 0.00 100.00
sda2 0.00 0.00 0.00 0.00 0.00 0.00 0.00
42949642.96 0.00 0.00 100.00
sdb 0.00 428.00 0.00 116.00 0.00
4368.00 37.66 2844.40 296.55 86.21 100.00
sdb1 0.00 428.00 0.00 116.00 0.00
4368.00 37.66 6874.40 296.55 86.21 100.00

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz
avgqu-sz await svctm %util
sda 0.00 0.00 0.00 0.00 0.00 0.00 0.00
42949552.96 0.00 0.00 100.00
sda1 0.00 0.00 0.00 0.00 0.00 0.00 0.00
42949662.96 0.00 0.00 100.00
sda2 0.00 0.00 0.00 0.00 0.00 0.00 0.00
42949642.96 0.00 0.00 100.00
sdb 4.00 182.00 6.00 77.00 80.00
2072.00 25.93 2814.50 54.22 120.48 100.00
sdb1 4.00 182.00 6.00 77.00 80.00
2072.00 25.93 6844.50 54.22 120.48 100.00

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz
avgqu-sz await svctm %util
sda 0.00 0.00 0.00 0.00 0.00 0.00 0.00
42949552.96 0.00 0.00 100.00
sda1 0.00 0.00 0.00 0.00 0.00 0.00 0.00
42949662.96 0.00 0.00 100.00
sda2 0.00 0.00 0.00 0.00 0.00 0.00 0.00
42949642.96 0.00 0.00 100.00
sdb 0.00 43.00 0.00
11.00 0.00 432.00 39.27 2810.40 36.36 909.09 100.00
sdb1 0.00 43.00 0.00
11.00 0.00 432.00 39.27 6840.40 36.36 909.09 100.00

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz
avgqu-sz await svctm %util
sda 0.00 15.84 0.00 17.82 0.00 269.31 15.11
42524309.47 44.44 561.11 100.00
sda1 0.00 15.84 0.00 17.82 0.00 269.31 15.11
42524419.47 44.44 561.11 100.00
sda2 0.00 0.00 0.00 0.00 0.00 0.00 0.00
42524398.67 0.00 0.00 100.00
sdb 0.99 222.77 0.99 114.85 15.84
2700.99 23.45 2814.16 35.90 86.32 100.00
sdb1 0.99 222.77 0.99 114.85 15.84
2700.99 23.45 6844.16 35.90 86.32 100.00

Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s avgrq-sz
avgqu-sz await svctm %util
sda 0.00 0.00 0.00 0.00 0.00 0.00 0.00
42949551.76 0.00 0.00 101.00
sda1 0.00 0.00 0.00 0.00 0.00 0.00 0.00
42949662.86 0.00 0.00 101.00
sda2 0.00 0.00 0.00 0.00 0.00 0.00 0.00
42949642.66 0.00 0.00 101.00
sdb 1.00 91.00 1.00
28.00 16.00 960.00 33.66 2838.40 10.34 348.28 101.00
sdb1 1.00 91.00 1.00
28.00 16.00 960.00 33.66 6908.70 10.34 348.28 101.00

The DB files and logs are on sdb1.

Can someone point me in the direction of some documentation on how to
interpret these numbers?

Also, I've tried to figure out what's getting cached by PostgreSQL by
looking at pg_statio_all_tables. What kind of ratio should I be seeing for
heap_blks_read / heap_blks_hit ?

Thanks.